U.S. patent number 6,677,992 [Application Number 09/176,966] was granted by the patent office on 2004-01-13 for imaging apparatus offering dynamic range that is expandable by weighting two image signals produced during different exposure times with two coefficients whose sum is 1 and adding them up.
This patent grant is currently assigned to Olympus Corporation. Invention is credited to Kuniaki Kami, Noboru Kusamura, Kanichi Matsumoto, Akihiko Mochida, Kotaro Ogasawara, Wataru Ohno, Katsuyuki Saito, Hideki Tashiro, Makoto Tsunakawa, Manabu Yajima, Shinji Yamashita.
United States Patent |
6,677,992 |
Matsumoto , et al. |
January 13, 2004 |
Imaging apparatus offering dynamic range that is expandable by
weighting two image signals produced during different exposure
times with two coefficients whose sum is 1 and adding them up
Abstract
An object is imaged continuously during a first exposure time
and a second exposure time shorter than the first exposure time.
Weights, one of which decreases monotonously and the other of which
increases monotonously, are applied to first and second resultant
image signals under the condition that the sum of the weights is 1.
The first and second image signals that have been weighted are
added up, thus producing a synthetic picture signal. When a
luminance level is low, the ratio of the first image signal, which
has been produced during the longer exposure time, to the second
image signal is increased. This results in an image demonstrating a
high signal-to-noise ratio. When the luminance level is high, the
ratio of the second image signal, which has been produced during
the shorter exposure time, to the first image signal is increased.
This results in a synthetic image that proves a wide dynamic range,
depicts a smoothly varying brightness level, and exhibits a
characteristic of being seen as almost natural. Moreover, the first
and second image signals are produced to resemble those produced
during mutually different exposure times by controlling an amount
of light incident on an imaging device or by varying an amount of
illumination light.
Inventors: |
Matsumoto; Kanichi (Hino,
JP), Saito; Katsuyuki (Sagamihara, JP),
Ogasawara; Kotaro (Tokyo, JP), Kami; Kuniaki
(Machida, JP), Yamashita; Shinji (Fuchu,
JP), Kusamura; Noboru (Hachioji, JP),
Mochida; Akihiko (Hino, JP), Ohno; Wataru
(Sagamihara, JP), Tsunakawa; Makoto (Toda,
JP), Tashiro; Hideki (Yokohama, JP),
Yajima; Manabu (Hino, JP) |
Assignee: |
Olympus Corporation
(JP)
|
Family
ID: |
27566842 |
Appl.
No.: |
09/176,966 |
Filed: |
October 22, 1998 |
Foreign Application Priority Data
|
|
|
|
|
Oct 23, 1997 [JP] |
|
|
9-291324 |
Nov 12, 1997 [JP] |
|
|
9-310774 |
Nov 12, 1997 [JP] |
|
|
9-310775 |
Nov 18, 1997 [JP] |
|
|
9-317401 |
Nov 27, 1997 [JP] |
|
|
9-326545 |
Dec 1, 1997 [JP] |
|
|
9-330439 |
Oct 20, 1998 [JP] |
|
|
10-298687 |
|
Current U.S.
Class: |
348/229.1;
348/299; 348/E5.034; 348/E5.038 |
Current CPC
Class: |
H04N
5/2258 (20130101); H04N 5/2354 (20130101); H04N
5/343 (20130101); H04N 5/35581 (20130101); H04N
5/372 (20130101); H04N 2005/2255 (20130101) |
Current International
Class: |
H04N
5/235 (20060101); H04N 5/225 (20060101); H04N
005/235 (); H04N 003/14 (); H04N 005/335 () |
Field of
Search: |
;348/299,298,230.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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57-39673 |
|
Mar 1982 |
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JP |
|
63-306779 |
|
Dec 1988 |
|
JP |
|
64-60156 |
|
Mar 1989 |
|
JP |
|
2-174470 |
|
Jul 1990 |
|
JP |
|
4-196776 |
|
Jul 1992 |
|
JP |
|
5-30424 |
|
Feb 1993 |
|
JP |
|
5-153473 |
|
Jun 1993 |
|
JP |
|
6-141229 |
|
May 1994 |
|
JP |
|
Primary Examiner: Christensen; Andrew
Assistant Examiner: Harris; Tia M.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen, LLP
Claims
What is claimed is:
1. An imaging apparatus comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time and a second image signal
produced by imaging said object during a time shorted than said
first exposure time; an image signal producing circuit composed of:
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level from a
light level of substantially no luminance up to a light level
causing said first and second image signals to have a saturation
value, and a second weight, which increases monotonously from said
light level of substantially no luminance up to said light level
causing said first and second image signals to have said saturation
value, to said first and second image signals under the condition
that the sum of said first and second weights is 1; and an adding
circuit for adding together first and second picture signals
produced by applying said first and second weights to said first
and second image signals by means of said first and second
weighting circuits; and a signal processing circuit for processing
a picture signal output from said adding circuit and producing a
video signal according to which an image can be displayed on a
display device.
2. An imaging apparatus according to claim 1, further comprising an
exposure time setting facility for varying at least one of said
first and second exposure times.
3. An imaging apparatus according to claim 2, wherein said exposure
time setting facility uses a waveform-detected signal produced by
detecting the waveform of said first or second image signal.
4. An imaging apparatus comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time, and a second image signal that
has a saturation value relative to a higher light level than said
first image signal; a picture signal producing device composed of:
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level from a
light level of substantially no luminance up to a light level
causing said first and second image signals to have the saturation
value, and a second weight, which increases monotonously from said
light level of substantially no luminance up to said light level
causing said first and second image signals to have said saturation
value, to said first and second image signals under the condition
that the sum of said first and second weights is 1; and an adding
circuit for adding together first and second picture signals
produced by applying said first and second weights to said first
and second image signals by means of said first and second
weighting circuits; and a signal processing circuit for processing
a picture signal output from said adding circuit and producing a
video signal according to which an image can be displayed on a
display.
5. An imaging apparatus according to claim 4, wherein said imaging
device images an object during a second exposure time that is
shorter than said first exposure time, and thus outputs said second
image signal that has the saturation value relative to a higher
light level than said first image signal.
6. An imaging apparatus according to claim 4, wherein during a
second exposure time during which said second image signal is
produced, an amount of light coming from said object and falling on
said imaging device through an imaging window is restricted by an
amount-of-light restricting device, and said imaging device outputs
said second image signal that has the saturation value relative to
a higher light level than said first image signal.
7. An imaging apparatus according to claim 4, wherein said weights
applied by said picture signal producing device are such that: when
a light level is much lower than the light level causing said first
image signal to have the saturation value, said first weight is
larger than said second weight; and when the light level is higher
than the light level causing said first image signal to have the
saturation value, said second weight is larger than said first
weight.
8. An imaging apparatus comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time, and a second image signal that
has a saturation value relative to a higher light level than said
first image signal; a picture signal producing device composed of:
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level up to
a light level causing said first and second image signals to have a
saturation value, and a second weight, which increases monotonously
therewith, to said first and second image signals under the
condition that the sum of said first and second weights is 1; and
an adding circuit for adding together first and second picture
signals produced by applying said first and second weights to said
first and second image signals by means of said first and second
weighting circuits; and a signal processing circuit for processing
a picture signal output from said adding circuit and producing a
video signal according to which an image can be displayed on a
display; wherein said first weight function F1(x) is cos.sup.2 (px)
where x is a light level and p is a coefficient, and said second
weight function F2(x) is sin.sup.2 (px).
9. An imaging apparatus according to claim 8, wherein said
coefficient p satisfies p.apprxeq..pi./(2s) where s is a light
level of light incident on said imaging device.
10. An imaging apparatus according to claim 4, wherein said imaging
device includes a progressive imaging device having two systems of
horizontal transfer output circuits.
11. An imaging apparatus according to claim 10, wherein said signal
processing means produces a video signal conformable to the
interlacing.
12. An imaging apparatus according to claim 4, wherein said image
signal producing circuit includes a weight data storage that stores
data of said first weight to be applied to said first image signal
and data of said second weight to be applied to said second image
signal.
13. An imaging apparatus according to claim 12, wherein said weight
data storage stores data of a weight to be applied to said first
image signal and data of a weight to be applied to said second
image signal, and the weights exhibit different
characteristics.
14. An imaging apparatus according to claim 13, further comprising
a brightness detector for detecting brightness information of an
object in an output signal of said imaging device, wherein a weight
to be applied to said first image signal and a weight to be applied
to said second image signal are selected based on the brightness
information of an object, and thus read from said weight data
storage.
15. An imaging apparatus according to claim 5, wherein said imaging
device images said object during said first exposure time, and
produces said first image signal and second image signal.
16. An imaging apparatus according to claim 4, wherein said picture
signal producing device produces a synthetic picture signal
exhibiting such a characteristic that a differential coefficient
thereof relative to a light level varies continuously with an
increase in light level up to a light level causing said second
image signal to have the saturation value.
17. An imaging apparatus according to claim 16, wherein the
differential coefficient decreases monotonously relative to the
light level.
18. An endoscopic imaging apparatus, comprising: an endoscope
having an elongated insertion unit, irradiating illumination light
to an object through an illumination window located at the distal
end of said insertion unit, and including an imaging device for
successively outputting a first image signal produced by imaging
said object illuminated with said illumination light during a first
exposure time, and a second image signal that has a saturation
value relative to a higher light level than said first image
signal; an image signal producing circuit composed of: first and
second weighting circuits for applying a first weight, which
decreases monotonously with an increase in light level from a light
level of substantially no luminance up to a light level causing
said first and second image signals to have the saturation value,
and a second weight, which increases monotonously from said light
level of substantially no luminance up to said light level causing
said first and second image signals to have said saturation value,
to said first and second image signals under the condition that the
sum of said first and second weights is 1; and an adding circuit
for adding together first and second picture signals produced by
applying said first and second weights to said first and second
image signals by means of said first and second weighting circuits;
a signal processing circuit for processing a picture signal output
from said adding circuit and producing a video signal which can be
displayed; and a display for displaying a synthetic image
represented by said picture signal when inputting said video
signal.
19. An endoscopic imaging apparatus according to claim 18, wherein
said imaging device images said object during a second exposure
time that is shorter than said first exposure time, and thus
outputs said second image signal that has the saturation level
relative to a higher light value than said first image signal.
20. An endoscopic apparatus according to claim 18, wherein during a
second exposure time during which said second image signal is
produced, an amount of light coming from said object and falling on
said imaging device through an imaging window is restricted by a
light restricting device, and said imaging device outputs said
second image signal that has the saturation value relative to a
higher light level than said first image signal.
21. An endoscopic imaging apparatus according to claim 18, further
comprising a light source unit for supplying illumination light to
a light guide that runs through said insertion unit of said
endoscope, propagates illumination light, and emits the
illumination light through said illumination window.
22. An endoscopic imaging apparatus according to claim 21, wherein
during a second exposure time during which said imaging device
produces a second image signal, said light source unit allows a
light restricting device to restrict illumination light to be
supplied to said light guide, and said imaging device outputs said
second image signal that has the saturation value relative to a
higher light level than said first image signal.
23. An endoscopic imaging apparatus according to claim 22, wherein
said light restricting device is a light restriction filter for
restricting illumination light generated by a lamp and supplying
resultant light to said light guide.
24. An endoscopic imaging apparatus according to claim 22, wherein
said light restricting device restricts an amount of illumination
light generated by a lamp.
25. An endoscopic imaging apparatus according to claim 18, wherein
said endoscope is an electronic endoscope and said imaging device
being provided with the ability to photoelectrically convert a
signal, placed on the image plane of an objective optical system
located at the distal end of said elongated insertion unit.
26. An endoscopic imaging apparatus according to claim 18, wherein
said endoscope is a TV camera-mounted endoscope composed of an
optical endoscope having an image propagating device for
propagating an object image formed by an objective optical system
located at the distal end of said elongated insertion unit to an
optical system, and a TV camera that is mounted on an eyepiece of
said optical endoscope and has an imaging device, which is included
in said imaging device and provided with the ability to
photoelectrically convert a signal, incorporated therein.
27. An endoscopic imaging apparatus according to claim 18, wherein
said endoscope includes a common image formation optical system,
and said imaging device is composed of a plurality of imaging
devices located at positions respectively at which a plurality of
images are formed through a plurality of apertures by said image
formation optical system.
28. An endoscopic imaging apparatus according to claim 19, wherein
said imaging device images said object during said first exposure
time so as to produce said first image signal and second image
signal.
29. An endoscopic imaging apparatus according to claim 18, wherein
said imaging device has a color separation filter used to achieve
color imaging under white illuminating light.
30. An endoscopic imaging apparatus according to claim 18, wherein
said imaging device is a field-sequential imaging device that
includes a monochrome imager not having a color separation filter,
and that carries out color imaging under illumination of
field-sequential light having a plurality of wavelengths.
31. An imaging apparatus, comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time, and a second image signal that
is produced by imaging said object during a second exposure time
shorter than said first exposure time and that has a saturation
value relative to a higher light level than said first image
signal; a picture signal producing circuit composed of: first and
second weighting circuits for applying a first weight, which
decreases monotonously with an increase in light level from a light
level of substantially no luminance up to a light level causing
said first and second image signals to have the saturation value,
and a second weight, which increases monotonously from said light
level of substantially no luminance up to said light level causing
said first and second image signals to have said saturation value,
to said first and second image signals under the condition that the
sum of said first and second weights is 1; and an adding circuit
for adding together first and second picture signals produced by
applying said first and second weights to said first and second
image signals by means of said first and second weighting circuits;
and a signal processing circuit for processing a picture signal
output from said adding circuit and producing a video signal
according to which an image can be displayed on a display.
32. An imaging apparatus, comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time, and a second image signal that
has a saturation value relative to a higher light level than said
first image signal; a picture signal producing circuit composed of:
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level from a
light level of substantially no luminance up to a light level
causing said first and second image signals to have the saturation
value, and a second weight, which increases monotonously from said
light level of substantially no luminance up to said light level
causing said first and second image signals to have said saturation
value, to said first and second image signals under the condition
that the sum of said first and second weights is 1; and an adding
circuit for adding together first and second picture signals
produced by applying said first and second weights to said first
and second image signals by means of said first and second
weighting circuits; and a signal processing circuit for processing
a picture signal output from said adding circuit and producing a
video signal according to which an image can be displayed on a
display.
33. An imaging apparatus, comprising: an imaging device for
successively outputting a first image signal produced by imaging an
object during a first exposure time, and a second image signal that
has a saturation value relative to a higher light level than said
first image signal; a picture signal producing circuit composed of:
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level from a
light level of substantially no luminance up to a light level
causing said first and second image signals to have the saturation
value, and a second weight, which increases monotonously from said
light level of substantially no luminance up to said light level
causing said first and second image signals to have said saturation
value, to said first and second image signals under the condition
that the sum of said first and second weights is 1; and an adding
circuit for adding together picture signals produced by applying
said first and second weights to said first and second image
signals by means of said first and second weighting circuits; and a
signal processing circuit for processing a picture signal output
from said adding circuit and producing a video signal according to
which an image can be displayed on a display.
34. An imaging apparatus according to claim 33, wherein when a
light level is higher than the light level causing said first image
signal to have the saturation value, said first weighting circuit
outputs a weight coefficient of 0.
35. An imaging apparatus according to claim 33, wherein when a
light level is higher than the light level causing said first image
signal to have the saturation value, said picture signal is
determined substantially with a weight coefficient that is applied
to said second image signal by said second weighting circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imaging apparatus offering a
dynamic range that is expandable by weighting a plurality of image
signals, which are produced during different exposure times or the
like, with a plurality of coefficients whose sum is 1, and adding
them up.
2. Description of the Related Art
In general, a range of luminance levels within which imaging is
validated by an imaging apparatus such as a TV camera is determined
unconditionally with the photoelectric conversion characteristic of
an imaging means, for example, a solid-stage imaging device.
Specifically, a lower limit of output levels of a solid-state
imaging device is determined by a noise level. An upper limit
thereof is determined by a saturation value. An operation range
within which the solid-state imaging device is usable is thus
defined. The slope of a characteristic curve expressing the output
levels of the solid-state imaging device is fixed to a certain
value. Eventually, the range of luminance levels within which
imaging is validated by the solid-state imaging device is
determined unconditionally.
For example, Japanese Unexamined Patent Publication No. 57-39673
has disclosed an imaging apparatus offering a dynamic range, which
is expandable by synthesizing image signals produced at two
different luminance levels, for an image signal produced by a
solid-state imaging device.
However, according to the prior art, the dynamic range offered by
the imaging apparatus is expanded merely by adding up two image
signals or subtracting one image signal from another. A
signal-to-noise ratio of a component of a resultant signal
indicating a low luminance level deteriorates. A synthetic picture
signal produced by synthesizing two image signals relative to
luminance levels is plotted as joined straight lines or a graph of
broken lines. This means that the synthetic image signal varies
according to the graph of broken lines. Since an output level of a
solid-state imaging device varies at a luminance level at which the
straight lines are joined, a constructed color image does not
depict a smooth color change but gives a sense of incongruity.
Moreover, according to Japanese Unexamined Patent Publication No.
6-141229, two or more image signals produced during different
charge accumulation times are weighted based on the signal levels,
and compressed by a compressing means. Thus, a picture signal whose
components range from a component representing a dark image to a
component representing a bright image will not have a saturation
value that can be constructed with few noises.
In the prior art, as shown in FIGS. 4 and 9 in the patent
publication, a plurality of image signals produced during different
charge accumulation times are weighted by varying a weight under a
boundary condition, under which one of the image signals has a
saturation value, or thereabout. Resultant image signals are then
synthesized by adding them up. The image signals are then
compressed by a compressing means according to a frequency band.
Eventually, a synthetic picture signal exhibiting a desired
input/output characteristic is constructed.
However, according to the prior art, for example, two image signals
are used to construct a synthetic picture signal. At this time, the
synthetic picture signal is constructed using only a first image
signal under conditions lower than the boundary condition under
which the first image signal produced during a longer charge
accumulation time has a saturation value.
The synthetic picture signal is compressed on a subsequent stage.
Since one synthetic picture signal resulting from addition is
compressed, the foregoing characteristic cannot be changed. For
example, when an image signal represents a motion, an image
reconstructed may suffer from inconsistency between contours
represented by a signal component indicating a low luminance level
and a signal component indicating a high luminance level. Besides,
the image has a portion in which colors change unnaturally.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an imaging
apparatus capable of offering an expandable dynamic range without
any deterioration of a signal-to-noise ratio of a signal component
indicating a low luminance level, and of constructing a smooth
image giving no sense of incongruity.
Another object of the present invention is to provide an endoscopic
imaging apparatus capable of offering an expandable dynamic range
without any deterioration of a signal-to-noise ratio of a signal
component indicating a low luminance level, and of constructing an
image suitable for diagnosis.
An imaging apparatus in accordance with the present invention
includes, an imaging means for successively outputting a first
image signal, which is produced by imaging an object during a first
exposure time, and a second image signal produced by imaging the
object during a time shorter than the first exposure time. The
invention includes a picture signal producing means composed of
first and second weighting circuits for applying a first weight,
which decreases monotonously with an increase in light level, and a
second weight, which increases monotonously therewith, to the first
and second image signals within the range of light levels up to
light levels, at which the first and second image signals have a
saturation value, under the condition that the sum of the first and
second weights is 1. Also included is an adding circuit for adding
up first and second picture signals produced by applying the first
and second weights to the first and second image signals by means
of the first and second weighting circuits. In addition, a signal
processing means is included for processing a picture signal output
from the adding circuit to produce a video signal based on which an
image can be displayed on a display means.
Owing to the above components, the ratio of the first image signal
to the second image signal can be modified, and the image signals
are synthesized with each other. Consequently, the dynamic range
for a picture signal is expanded, and deterioration of a
signal-to-noise ratio of a signal component indicating a low
luminance level is prevented. This results in a natural smooth
image not giving a sense of incongruity.
Moreover, when the present invention is adapted to an endoscopic
imaging apparatus, an image helpful for diagnosis can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 7 relate to the first embodiment of the present
invention;
FIG. 1 is a diagram showing a configuration of an imaging apparatus
of the first embodiment;
FIG. 2 is a diagram showing a configuration of a red dynamic range
expanding circuit shown in FIG. 1;
FIG. 3A is a diagram showing memory maps of first and second
look-up tables shown in FIG. 2;
FIG. 3B is an explanatory diagram graphically showing weight
coefficients output from the first and second look-up tables in
relation to an input signal;
FIGS. 4A to 4I are timing charts indicating timing of each signal
produced by the red dynamic range expanding circuit shown in FIG.
2;
FIG. 5 is an explanatory diagram for explaining the operation of
the red dynamic range expanding circuit shown in FIG. 2;
FIG. 6 is a diagram showing a configuration of a red dynamic range
expanding circuit of a variant;
FIG. 7 is a diagram showing a configuration of a red dynamic range
expanding circuit in the variant;
FIGS. 8A to 10 relate to the second embodiment of the present
invention;
FIG. 8A is a diagram showing a configuration of a red dynamic range
expanding circuit in the second embodiment;
FIG. 8B is a diagram showing a memory map of first and second
look-up tables shown in FIG. 8A;
FIGS. 9A to 9I are timing charts indicating timing of each signal
produced by the red dynamic range expanding circuit shown in FIG.
8A;
FIG. 10 is a graph showing a characteristic concerning brightness
of an output that is a synthetic picture signal produced according
to a variant;
FIGS. 11 to 17 relate to the third embodiment of the present
invention;
FIG. 11 is a block diagram showing a configuration of an imaging
apparatus of the third embodiment;
FIG. 12 is a block diagram showing a configuration of a dynamic
range expanding circuit;
FIG. 13 is a graph indicating input/output characteristics relative
to a low shutter speed shutter and high shutter speed, and an
input/output characteristic attained by selecting a mixed function
to expand a dynamic range;
FIG. 14 is a diagram showing existence of a plurality of functions
in each of the look-up tables;
FIGS. 15A to 15K are timing charts for explaining actions;
FIG. 16 is a block diagram showing a configuration of a dynamic
range expanding circuit in a variant of the first embodiment;
FIG. 17 is a graph showing a characteristic that can be selected to
expand a dynamic range according to the variant;
FIGS. 18 to 22 relate to the fourth embodiment of the present
invention;
FIG. 18 is a block diagram showing a configuration of an imaging
apparatus of the fourth embodiment;
FIG. 19 is a diagram showing a structure of a progressive
charge-coupled device;
FIG. 20 is a timing chart indicating output signals in a wide
dynamic range mode;
FIG. 21 is a timing chart indicating an output in a normal
mode;
FIG. 22 is a graph indicating an input/output characteristic
attained by processing outputs produced at a high shutter speed
shutter and low shutter speed so as to expand a dynamic range;
FIGS. 23 to 25 relate to the fifth embodiment of the present
invention;
FIG. 23 is a diagram showing a configuration of an endoscopic
imaging apparatus of the fifth embodiment;
FIG. 24 is a timing chart indicating an operation exerted by the
endoscopic imaging apparatus;
FIG. 25 is a characteristic graph indicating the output levels of
image signals produced by first and second charge-coupled devices,
and the output level of a synthetic picture signal produced by an
adding circuit in relation to an amount of incident light;
FIGS. 26 and 27 relate to the sixth embodiment of the present
invention;
FIG. 26 is a block diagram showing a configuration of an imaging
apparatus of the sixth embodiment;
FIG. 27 is a timing chart indicating field by field the
relationships among an output of a charge-coupled device, an output
of a waveform detecting circuit, and data produced by a
charge-coupled device shutter;
FIGS. 28 and 29 relate to the seventh embodiment of the present
invention;
FIG. 28 is a block diagram showing a configuration of an imaging
apparatus of the seventh embodiment;
FIG. 29 is a timing chart indicating field by field the
relationships among an output of a charge-coupled device, an output
of a waveform detecting circuit, and data produced by a
charge-coupled device shutter;
FIGS. 30 and 31 relate to the eighth embodiment of the present
invention;
FIG. 30 is a block diagram showing a configuration of an imaging
apparatus of the eighth embodiment;
FIG. 31 is a timing chart indicating field by field the
relationships among an output of a charge-coupled device, an output
of a waveform detecting circuit, and data produced by a
charge-coupled device shutter;
FIG. 32 is a timing chart indicating an output of a charge-coupled
device for each field in a variant of the eighth embodiment;
FIGS. 33 to 40G relate to the ninth embodiment of the present
invention;
FIG. 33 is a diagram schematically showing an endoscopic imaging
apparatus of the ninth embodiment;
FIG. 34 is a diagram showing a practical configuration of an
endoscopic imaging unit;
FIGS. 35A and 35B are diagrams showing a filter member;
FIG. 36 is a graph indicating characteristics attained when two
filters are used for imaging;
FIGS. 37A to 37C are explanatory diagrams for explaining the action
of a filter or the like, which is located on an optical path,
according to a field judgment signal;
FIG. 38 is a block diagram showing a configuration of a video
processor serving as an image processing unit;
FIG. 39 is a block diagram showing a configuration of a dynamic
range expanding unit;
FIGS. 40A to 40G are timing charts for explaining the actions of
the dynamic range expanding unit;
FIGS. 41 to 52 relate to the tenth embodiment of the present
invention;
FIG. 41 is a diagram showing a practical configuration of a
field-sequential type endoscopic imaging unit of the tenth
embodiment;
FIG. 42 is a diagram showing an RGB rotary filter;
FIG. 43 is a diagram showing a filter member;
FIG. 44 is a block diagram showing a configuration of a video
processor serving as an image processing unit;
FIGS. 45A to 45F are explanatory diagrams indicating the actions of
an endoscopic imaging unit;
FIG. 46 is a block diagram showing a configuration of a dynamic
range expanding unit;
FIGS. 47A to 47I are explanatory diagrams indicating the actions of
a signal selector interpolator;
FIGS. 48A and 48E are explanatory diagrams indicating the actions
of an imaging unit in the first variant;
FIG. 49 is a diagram showing a filter member in the second
variant;
FIGS. 50A to 50I are explanatory diagrams indicating the actions of
an imaging unit;
FIGS. 51A to 51I are explanatory diagrams indicating the actions of
a signal selector interpolator;
FIG. 52 is a block diagram schematically showing a configuration of
a signal selector and interpolator;
FIGS. 53 to 55C relate to the eleventh embodiment of the present
invention;
FIG. 53 is a diagram showing part of an imaging unit in the
eleventh embodiment;
FIGS. 54A to 54C are explanatory diagrams indicating the actions of
the imaging unit;
FIGS. 55A to 55C are explanatory diagrams for explaining the
actions of an imaging unit in a variant of the eleventh
embodiment;
FIGS. 56 to 59 relate to the twelfth embodiment of the present
invention;
FIG. 56 is a diagram schematically showing a configuration of an
endoscopic imaging apparatus of the twelfth embodiment;
FIGS. 57A and 57B are diagrams showing a configuration of a light
source unit and a filter member;
FIGS. 58A to 58C are explanatory diagrams indicating the actions of
a unit for controlling an amount of emitted light;
FIG. 59 is a diagram showing a configuration of a light source unit
in a variant of the twelfth embodiment;
FIGS. 60 to 61D relate to the thirteenth embodiment of the present
invention;
FIG. 60 is a diagram schematically showing a configuration of an
endoscopic imaging apparatus of the thirteenth embodiment; and
FIGS. 61A to 61D are explanatory diagrams indicating the actions of
a unit for controlling an amount of emitted light.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, embodiments of the present invention
will be described below.
First Embodiment
As shown in FIG. 1, an imaging apparatus 1 of this embodiment
consists of a charge-coupled device (CCD) 2, a synchronizing
(hereinafter, sync) signal generating circuit (SSG) 3, a timing
generator 4, and a CCD driver 5. The CCD 2 is a single-plate color
imaging device for imaging an object. The SSG generates a reference
signal. The timing generator 4 inputs the reference signal sent
from the SSG 3 and produces a driving signal or the like used to
drive the CCD 2. The CCD driver drives the CCD 2 in response to the
driving signal sent from the timing generator 4.
The imaging apparatus 1 further includes a preamplifier 6, a CDS
circuit 7, and an A/D converter 8. The preamplifier 6 amplifies an
image signal sent from the CCD 2. The CDS circuit 7 carries out
correlative double sampling (CDS) according to a sampling pulse
sent from the timing generator 4. The A/D converter 8 converts an
analog signal output from the CDS circuit 7 into a digital signal.
After an image signal output from the CCD 2 is amplified by the
preamplifier 6, the frequency of the image signal is lowered to the
baseband by the CDS circuit 7. The resultant signal is converted
into a digital signal by the A/D converter 8. The A/D converter 8
converts an analog signal into a digital signal of 8 bits long.
Furthermore, the imaging apparatus 1 includes a color separating
circuit 9, a white balance circuit 10, an automatic gain control
circuit (hereinafter, AGC circuit) 11, a knee and gamma circuit 12,
a red dynamic range expanding circuit 15R, green dynamic range
expanding circuit 15G, and blue dynamic range expanding circuit
15B, an enhancing circuit 16, and a D/A converter 18. Specifically,
the color separating circuit 9 separates three color-signal
components representing red, green and blue from a digital signal
produced by the A/D converter 8. The white balance circuit 10
adjusts a white balance indicated by each of digital signals that
are the color-signal components separated by the color separating
circuit 9. The AGC circuit 11 adjusts a gain to be given to each of
the digital signals whose white balance has been adjusted by the
white balance circuit 10. The knee and gamma circuit 12 treats a
knee of a curve plotted based on each of the digital signals whose
gain has been adjusted by the AGC circuit 11, and corrects a gamma
indicated by the digital signal. The red dynamic range expanding
circuit 15R, green dynamic range expanding circuit 15G, and blue
dynamic range expanding circuit 15B expand dynamic ranges for the
red, green, and blue digital signals that have been processed to
treat a knee and correct a gamma. The enhancing circuit 16 enhances
the red, green, and blue digital signals for which dynamic ranges
have been expanded by the red dynamic range expanding circuit 15R,
green dynamic range expanding circuit 15G, and blue dynamic range
expanding circuit 15B respectively. The D/A converter 18 converts
the digital signals, which have been enhanced by the enhancing
circuit 16, into analog signals, and outputs the analog signals to
a monitor 19 via a 75.OMEGA. driver 17.
The red dynamic range expanding circuit 15R includes, as shown in
FIG. 2, a field memory 21, and a first selector 22 and second
selector 23. Specifically, the field memory 21 stores a digital
signal of a red signal rendering one field and being processed to
treat a knee and correct a gamma by the knee and gamma circuit 12.
The first selector 22 and second selector 23 select and output
either of a red signal rendering a previous field and a red signal
rendering a current field, which are stored in the field memory 21,
according to a field judgment signal sent from the timing generator
4. The second selector 23 is connected to the first selector 22 via
an inverter 24. The second selector 23 therefore outputs a red
signal rendering a field different from the previous field or
current field represented by a red signal output from the first
selector 22.
The red dynamic range expanding circuit 15R consists of a first
look-up table (hereinafter, first LUT) 25 and second LUT 26, a
first multiplier 27, a second multiplier 28, and an adder 29.
Specifically, a given function, which will be described later,
specified by the level of a portion of an output, that is, a red
signal component of the second selector 23 is read from the first
LUT 25 and second LUT 26. Herein, the red signal component renders
a pixel. The first multiplier 27 multiplies the red signal
component, which receives from the first selector 22 and renders a
pixel, by an output of the first LUT 25. The second multiplier 28
multiplies, the red signal component, which receives from the
second selector 23 and renders a pixel, by an output of the second
LUT 26. The adder 29 adds up an output of the first multiplier 27
and an output of the second multiplier 28, and outputs a result to
the enhancing circuit 16.
The green dynamic range expanding circuit 15G and blue dynamic
range expanding circuit 15B have the same circuitry as the red
dynamic range expanding circuit 15R. The description of their
configurations will therefore be omitted.
The first LUT 25 and second LUT 26 are memory maps like the ones
shown in FIG. 3A.
In the first LUT 25 and second LUT 26, a weight coefficient
f=cos.sup.2 that decreases monotonously, and a weight coefficient
g=sin.sup.2 that increases monotonously are stored at addresses 00
to FF. The addresses are each, for example, 8 bits long. The data
of the weight coefficients or functions f and g is set so that the
sum thereof will be 1.
Now, the addresses 00 to FF each having a length of 8 bits are
associated with luminance levels indicated by a 8-bit input digital
signal. More particularly, assume that an image signal produced by
the CCD 2 indicates a luminance level 0, and the image signal is
converted into a digital signal by the A/D converter 8. In this
case, an address 00h is referenced in the first LUT 25 and second
LUT 26.
As shown in FIG. 1, an output signal of the CCD 2, that is, an
image signal is amplified and corrected in terms of a gamma by the
AGC circuit 11 and others. The signal level is adjusted according
to the dynamic range permitted by the display screen of the monitor
19.
In other words, when an output signal of the CCD 2 indicates a
luminance level 0, the level of a signal input to the monitor 19 is
also 0. When the CCD 2 is saturated, the level of an image signal
output to the monitor is adjusted to have a saturation value (Vuse
in FIG. 5).
Moreover, when an image signal that is an output signal of the CCD
2 has a saturation value (for example, Vuse in FIG. 5), the image
signal is sent to the A/D converter 8 and others. An address FFh is
then referenced in the first LUT 25 and second LUT 26.
Incidentally, for example, 00h means 00 in hexadecimal
notation.
A signal x based on which the first LUT 25 and second LUT 26 are
referenced may be standardized to represent a value ranging from 0
to 1 (namely, a digital value 00h is associated with 0 and a
digital value FFh is associated with 1). In this case, cos.sup.2
(px) is read from the first LUT 25 and sin.sup.2 (px) is read from
the second LUT 26.
Based on a signal x based on which the first LUT 25 and second LUT
26 are referenced, data is read from an associated address. The
reading is illustrated in FIG. 3B.
In FIG. 3B, p denotes a correction coefficient. Assume that a
brightness level at which an image signal, which is produced by
imaging an object during a short exposure time, has a saturation
value of ys2. The correction coefficient p is set to a value
causing the weight function g, that is, sin.sup.2 (px) to have 1
relative to the brightness level of ys2, for example,
p=(.pi..multidot.ys2/2).
Next, the operations of the imaging apparatus 1 of this embodiment
having the foregoing components will be described.
A driving signal is produced by the timing generator 4 according to
a reference signal sent from the SSG 3. With the driving signal,
the CCD driver 5 drives the CCD 2. A photoelectrically converted
signal of an object produced by the CCD 2 is amplified by the
preamplifier 6. The frequency of the signal is then lowered to fall
within the baseband by the CDS circuit 7. The resultant signal is
then converted into a digital signal by the A/D converter 8.
With the driving signal generated by the timing generator 4, the
CCD driver 5 drives the CCD 2. When driven, the CCD 2 will image an
object at a shutter speed that is different from field to field,
for example, a first shutter speed of 1/60 sec. Otherwise, the CCD
2 will image the object using a high-speed device shutter at a
second shutter speed that is, for example, a quadruple of the first
shutter speed (that is, 1/240 sec).
In other words, an object image rendering field A is produced at
the first shutter speed. An object image rendering field B is
produced at the second shutter speed. For field B, an image signal
produced by exposing an object for a period of time other than
1/240 sec during one field period (1/60 sec) is swept away
quickly.
As described later, image signals produced by imaging an object at
different shutter speeds are processed by the red dynamic range
expanding circuit 15R, green dynamic range expanding circuit 15G,
and blue dynamic range expanding circuit 15B. Thus, the dynamic
ranges for red, green, and blue signals are expanded.
Thereafter, three color-signal components of red, green, and blue
are separated from a digital signal, which has been converted from
an analog signal, by the color separating circuit 9. On the three
resultant digital signals, white balance adjustment, gain control,
knee treatment, and gamma correction are performed by the white
balance circuit 10, AGC circuit 11, and knee and gamma circuit 12
respectively. Thereafter, the red dynamic range expanding circuit
15R, green dynamic range expanding circuit 15G, and blue dynamic
range expanding circuit 15B expand the dynamic ranges for the red,
green, and blue digital signals. The enhancing circuit 16 enhances
the digital signals. The D/A converter 18 converts the digital
signals into analog signals. The analog signals are output to the
monitor 19 via the 75.OMEGA. driver 17.
Next, dynamic range expansion processing to be performed by the red
dynamic range expanding circuit 15R, green dynamic range expanding
circuit 15G, and blue dynamic range expanding circuit 15B will be
detailed. Referring to the timing chart of FIGS. 4A to 4I, dynamic
range expansion processing will be described by taking the red
dynamic range expanding circuit 15R for instance.
A field judgment signal (FIG. 4B) is synchronous with a vertical
sync signal VD (FIG. 4A) contained in a video signal. The field
judgment signal is output from the timing generator 4 to the second
selector 23 via the first selector 22 and inverter 24 in the red
dynamic range expanding circuit 15R.
Moreover, a red output of the knee and gamma circuit 12 is applied
to one input terminal of the first selector 22 and second selector
23 in the red dynamic range expanding circuit 15R. An output of the
field memory 21 (FIG. 4D) is applied to the other input terminal of
the first selector 22 and second selector 23.
Based on the field judgment signal, a digital signal produced at
the first shutter speed (1/60 sec) to render field A is output from
the first selector 22. A digital signal produced at the second
shutter speed (1/240 sec) to render field B is output from the
second selector 23.
The digital signal rendering field A from the first selector 22 is
output to the first multiplier 27. The digital signal rendering
field B from the second selector 23 is output to the second
multiplier 28, first LUT 25 (FIG. 4E), and second LUT 26 (FIG.
4F).
At this time, based on a signal x that is a digital image signal
component rendering a pixel of field B and cos.sup.2 (px) is output
from the first LUT 25 and a digital image signal component
rendering a pixel of field B and sin.sup.2 (px) is output from the
second LUT 26.
In this case, an image signal rendering field A is produced by
imaging an object during an exposure time (imaging time) that is
four times longer than the exposure time during which an image
signal rendering field B is produced. As shown in FIG. 5, the image
signal exhibits a characteristic x1=y relative to a brightness
level y of the object. By contrast, an image signal rendering field
B exhibits a characteristic x2=y/4.
The image signal x1 rendering field A has a saturation value Vuse
relative to a brightness level ys1. The image signal x2 rendering
field B has the saturation value Vuse relative to a brightness
level ys2 (=4ys1).
In this embodiment, assume that an image signal x1 produced at a
brightness level ya to render field A has, for example, a value x1a
in FIG. 5. In this case, an image signal rendering field B has a
value x2a.
As shown in FIG. 3B, the first LUT 25 and second LUT 26 are
referenced based on the image signal x2 rendering field B. Weight
functions of f=cos.sup.2 (px) and g=sin.sup.2 (px) are then read
out.
The functions cos.sup.2 (px) and sin.sup.2 (px) are output to the
first multiplier 27 and second multiplier 28. The first multiplier
27 multiplies a digital image signal component, which renders a
pixel of field A, by cos.sup.2 (px) (FIG. 4G). The second
multiplier 28 multiplies a digital image signal component, which
renders a pixel of field B, by sin.sup.2 (px) (FIG. 4H).
The adder 29 adds up an output of the first multiplier 27 and an
output of the second multiplier (FIG. 4I).
In FIGS. 4A to 4I, for brevity's sake, an output rendering each
pixel of field A is denoted by An, and an output rendering each
pixel of field B is denoted by Bn. Dynamic range expansion
processing in this embodiment is, as mentioned above, carried out
in units of a pixel. Assume that an output value that is a digital
image signal component rendering each pixel of field A is x, and an
output value that is a digital image signal component rendering
each pixel of field B is u. An output M of the adder 29 is
expressed as follows:
The green dynamic range expanding circuit 15G and blue dynamic
range expanding circuit 15B act similarly to the red dynamic range
expanding circuit 15R. The description of the expanding circuits
will therefore be omitted.
According to this embodiment, as shown in FIG. 5, the digital image
signal x1 is produced at the first shutter speed (1/60 sec) to
render field A. The digital image signal x2 (=u) is produced at the
second shutter speed (1/240 sec) to render field B. When a
luminance level is low, the output M of the red dynamic range
expanding circuit 15R is dominated by the digital image signal x1
weighted with cos.sup.2 (px). When a luminance level is high, the
output M is dominated by the digital image signal x2 weighted with
sin.sup.2 (px). Thus, a dynamic range can be expanded without any
deterioration of a signal-to-noise ratio of a picture signal
component indicating a low luminance level.
For more details, referring to FIG. 5, the output M corresponding
to a synthetic picture signal produced by weighting two picture
signals and adding them up will be studied. When a brightness level
is, for example, higher than 0 and much lower than ys1, the weight
f for the picture signal rendering field A is larger. The weight g
for the picture signal rendering field B is smaller. That is to
say, f>g>0 is established. The synthetic picture signal is a
synthetic picture signal produced by slightly mixing the picture
signal rendering field B in the picture signal rendering field A
with pixel locations matched.
Moreover, when a brightness level is higher than ys1, the picture
signal rendering field A has a saturation value. The weight f for
the picture signal having the saturation value is smaller. By
contrast, the weight g for the picture signal rendering field B is
larger. Namely, g>f>0 is established. The synthetic picture
signal is therefore produced by slightly mixing the saturation
value of the picture signal rendering field A in the picture signal
rendering field B. The synthetic picture signal exhibits a
characteristic of indicating a luminance level that increases
smoothly with an increase in brightness level of an object.
In other words, according to the first embodiment, a first image
signal that has a saturation value relative to a first brightness
level ys1 is weighted with a weight coefficient f that decreases
monotonously. A second image signal that has a saturation value
relative to a second brightness level ys2 higher than the first
brightness level ys1 (four times higher than ys1 in FIG. 5) is
weighted with a weight coefficient g that increases monotonously.
Resultant picture signals are added up by an adder. Thus, a
synthetic picture signal is produced.
In this embodiment, the sum of the weight coefficients f and g is
retained at 1. It is thus prevented that the level of a synthetic
picture signal resulting from addition gets larger after passing
through a dynamic range expanding circuit, and thus exceeds the
level of a picture signal to be output to the monitor 19 which is a
saturation value. In other words, when the sum exceeds 1, a
compression circuit must be installed on a stage succeeding the
dynamic range expanding circuit. This embodiment obviates the
necessity of the compression circuit.
Moreover, referring to FIG. 5, the output Ma corresponding to a
synthetic picture signal is produced by weighting the image signal
x1a, and the image signal x2a with the weight coefficients f and g,
and adding them up. Herein, the image signal x1a is produced at a
brightness level ya in order to render field A. The image signal
x2a renders field B. The level of the output Ma is determined by
adopting the levels of the signals x1a and x2a according to a ratio
proportional to the ratio of the inverse value of the weight
coefficient f, 1/f, to the inverse value of the weight coefficient
g, 1/g.
Moreover, as seen from FIG. 5, the output M may be regarded as a
function of a brightness level that is a variable. The derived
function of the function is positive and decreases monotonously.
That is to say, the gradient of the derived function is increased
relative to low brightness levels. The gradient is decreased
continuously with a rise in brightness level. This results in a
wider dynamic range.
A thus produced synthetic picture signal can be expressed as a
function that increases continuously smoothly and monotonously by
setting the coefficient p properly relative to the image signal x.
At this time, the function increases within the range of brightness
levels up to a brightness level at which a signal produced at a
second shutter speed has a saturation value. Consequently, a
natural image not giving a sense of incongruity can be viewed. In
other words, according to this embodiment, the synthetic picture
signal M is produced by weighting two whole image signals (one
image signal has a saturation value) and adding them up. This
embodiment can therefore offer a wide dynamic range that is wide
enough to produce a synthetic picture signal similar to a picture
signal produced by performing imaging once. Moreover, a picture
signal exhibiting a characteristic of indicating a luminance level
that changes smoothly with an increase in brightness of an object
can be produced to display a natural good-quality image. Moreover,
even when an object makes a motion, inconsistency between a contour
depicted by a picture signal component indicating a low luminance
level and a contour depicted by another component indicating a high
luminance level is minimized.
Moreover, in this embodiment, two image signals are weighted with
weight coefficients and then added up. The sum of the weight
coefficients f and g is set to 1. A picture signal resulting from
addition enjoys a wide dynamic range ending with the signal level
of an image signal rendering field B which is a saturation value.
Moreover, it will not take place that the signal level is raised
before and after the image signal passes through the dynamic range
expanding circuit 15R or the like.
By contrast, according to the prior art disclosed in the Japanese
Unexamined Patent Publication No. 6-141229, a different weight is
applied under a condition close to a boundary condition under which
one of two image signals has a saturation value. Image signals
weighted are then added up. The signal level of a resultant picture
signal relative to a condition away from the boundary condition
becomes a several multiple of the signal level thereof attained
under the boundary condition. A compression circuit for compressing
a synthetic picture signal must therefore be installed on a
succeeding stage.
Moreover, the compression circuit is used to compress a synthetic
picture signal so that the signal will exhibit a characteristic
that the signal level varies continuously with an increase in
brightness. In this case, the compression circuit must incur a
large load.
In this embodiment, the correction coefficient p is set as
p.apprxeq.(.pi..multidot.ys2/2). Aside from this, the correction
coefficient p may be set to any value causing the output M to
increase monotonously with an increase in brightness according to
the characteristics of the CCD. Moreover, the output M is not
limited to the function x cos.sup.2 (px)+usin.sup.2 (px).
Alternatively, the output M may be a function constructing a
synthetic picture signal, which is dominated by an image signal
produced at a low shutter speed, relative to a low luminance level.
Relative to a high luminance level, the function constructs a
synthetic picture signal dominated by an image signal produced at a
high shutter speed.
In FIG. 5, for brevity's sake, the signals x1 and x2 vary linearly
relative to a brightness level y. This embodiment can also be
adapted to an imaging apparatus in which the signals vary
non-linearly.
In this embodiment, the color separating circuit 9 separates red,
green, and blue color signal components. The red dynamic range
expanding circuit 15R, green dynamic range expanding circuit 15G,
and blue dynamic range expanding circuit 15B expand the dynamic
ranges for the red, green, and blue signals. The present invention
is not limited to this mode. Alternatively, the color separating
circuit may separate a luminance signal and chrominance signal. The
dynamic ranges for both the luminance signal and chrominance signal
or the dynamic range for only the luminance signal may be
expanded.
In this embodiment, after color signal components are separated,
the dynamic ranges for the signals are expanded. The present
invention is not limited to this mode. Alternatively, as shown in
FIG. 6, the red dynamic range expanding circuit 15R, green dynamic
range expanding circuit 15G, and blue dynamic range expanding
circuit 15B may be unused. Instead, a dynamic range expanding
circuit 40 may be installed on a stage succeeding the A/D converter
8 for converting an analog signal into a digital signal. The
dynamic range for a signal that has just been digitized may be
expanded. In this case, the other components are identical to those
of this embodiment.
In the first embodiment, the weight coefficients f and g are
determined with an image signal rendering field B. Alternatively,
they may be determined with both image signals rendering fields A
and B. In this case, the red dynamic range expanding circuit 15R
has a configuration shown in FIG. 7.
In FIG. 2, an output of the second selector 23 is input to the
first and second LUTs 25 and 26. In FIG. 7, an output of the first
selector 22 is input to the first LUT 25, and an output of the
second selector 23 is input to the second LUT 26. The other
connections are identical to those shown in FIG. 2.
In FIG. 7, a weight coefficient f is read from the first LUT 25
according to an image signal rendering field A. A weight
coefficient g is read from the second LUT 26 according to an image
signal rendering field B.
Even in this variant, the weight coefficients f and g are
f=cos.sup.2 (px) and g=sin.sup.2 (px). Herein, px is defined within
a range of brightness levels ys2 associated with a range from a
level 0 of the second image signal x2 to a level of a saturation
value thereof.
In this variant, when an imaging condition becomes different
between fields A and B (for example, a brightness level of an
object becomes different between fields A and B), the sum of the
weight coefficients f and g may not be 1. Herein, the weight
coefficient f is read based on the level of the first image signal
x1 rendering field A. The weight coefficient g is read based on the
level of the second image signal x2 rendering field B. In this
case, therefore, f+g=1 is established. By contrast, in the first
embodiment, the two weight coefficients f and g are determined
based on the level of one image signal. f+g=1 can be satisfied.
Second Embodiment
The second embodiment is substantially identical to the first
embodiment. Only a difference will be described. The same reference
numerals will be assigned to the same components. The description
of the components will be omitted.
The red dynamic range expanding circuit 15R in this embodiment
includes, as shown in FIG. 8A, the field memory 21, a selector 41,
a first LUT 42, and a second LUT 44. Specifically, the field memory
21 stores a digital red signal rendering one field and having been
processed to treat a knee and correct a gamma by the knee and gamma
circuit 12. The selector 41 selects and outputs either of a red
signal rendering a previous field and a red signal rendering a
current field, which are stored in the field memory 21, according
to a field judgment signal sent from the timing generator 4. The
field judgment signal is input as a high-order address bit into the
first LUT 42. A given function that will be described later is
output from the first LUT 42 according to the level of an output
signal rendering a pixel. The field judgment signal is input as a
high-order address bit into the second LUT 44 via an inverter 43. A
given function that will be described later is output from the
second LUT 44 according to the level of an output signal rendering
a pixel. The first multiplier 27 multiplies the red signal output
from the field memory 21 by the output signal rendering a pixel and
an output of the first LUT 42. The second multiplier 28 multiplies
the red signal output from the knee and gamma circuit 12 by the
output signal rendering a pixel and an output of the second LUT 44.
The adder 29 adds up outputs of the first multiplier 27 and second
multiplier 28, and outputs a resultant signal to the enhancing
circuit 16.
When an image signal produced at the first shutter speed (1/60 sec)
to render field A is output from the field memory 21, the selector
41 selects an image signal rendering field B which is output from
the knee and gamma circuit 12. The field judgment signal is input
as a high-order address bit "0" to the first LUT 42. The field
judgment signal is input as a high-order address bit "1" to the
second LUT 44 via the inverter 43.
When an image signal produced at the second shutter speed (1/240
sec) to render field B is output from the field memory 21, the
selector 41 selects the image signal rendering field B. The field
judgment signal is input as a high-order address bit "1" to the
first LUT 42. The field judgment signal is input as a high-order
address bit "0" to the second LUT 44 via the inverter 43.
The green dynamic range expanding circuit 5G and blue dynamic range
expanding circuit 15B have the same circuitry as the red dynamic
range expanding circuit 15R of this embodiment. The description of
the circuits will be omitted.
The foregoing first LUT 42 and second LUT 44 are, as shown in FIG.
8B, defined in a common memory map. When the high-order address bit
"0" is input, cos.sup.2 (px) where x denotes the level of the
output signal rendering a pixel is output. When the high-order
address bit "1" is input, sin.sup.2 (px) where x denotes the level
of the output signal rendering a pixel is output.
The other components are identical to those of the first
embodiment.
Next, the operations of this embodiment will be described with
reference to the timing charts of FIGS. 9A to 9I.
A field judgment signal (FIG. 9B) synchronous with a video signal
VD (FIG. 9A) is output from the timing generator 4 to the selector
41 and first LUT 42 in the red dynamic range expanding circuit 15R.
The field judgment signal is also output to the second LUT 44 via
the inverter 24 therein.
A red output of the knee and gamma circuit 12 is input to the field
memory 21 (FIG. 9C), selector 41, and second multiplier 28 in the
red dynamic range expanding circuit 15R. An output of the field
memory (FIG. 9D) is input to the selector 41 and first multiplier
27.
Assume that a digital image signal rendering field A is stored in
the field memory 21. In this case, a digital image signal rendering
field B is output from the knee and gamma circuit 12 to the first
LUT 42 and second LUT 44 via the selector 41 in response to the
field judgment signal. At this time, a high-order address bit "0"
is input into the first LUT 42. cos.sup.2 (px) where x denotes the
level of an output rendering a pixel is output (FIG. 9E). A
high-order address bit "1" is input into the second LUT 44.
sin.sup.2 (px) where x denotes the level of an output rendering a
pixel is output (FIG. 9F).
The first multiplier 27 multiplies the digital image signal
rendering a pixel of field A by cos.sup.2 (px) (FIG. 9G). The
second multiplier 28 multiplies the digital image signal rendering
a pixel of field B by sin.sup.2 (px) (FIG. 9H).
Assume that a digital image signal rendering field B is stored in
the field memory 21. In this case, the digital image signal
rendering field B is output from the field memory 21 to the first
LUT 42 and second LUT 44 via the selector 44 in response to a field
judgment signal. At this time, a high-order address bit "1" is
input into the first LUT 42. sin.sup.2 (px) where x denotes the
level of an output rendering a pixel is output (FIG. 9E). A
high-order address bit of "0" is input into the second LUT 44.
cos.sup.2 (px) where x denotes the level of an output rendering a
pixel is output (FIG. 9F).
The multiplier 27 multiplies the digital image signal rendering a
pixel of field B by sin.sup.2 (px) (FIG. 9G). The second multiplier
28 multiplies the digital image signal rendering a pixel of field A
by cos.sup.2 (px) (FIG. 9H).
The adder 29 adds up an output of the first multiplier 27 and an
output of the second multiplier 28 (FIG. 9I).
The other components are identical to those of the first
embodiment.
Even in this embodiment, the same advantages as those provided by
the first embodiment can be provided.
As mentioned above, according to the first and second embodiments
and variant, a picture signal producing means changes the ratio of
a first image signal to a second image signal according to a light
level incident on an imaging means. The picture signal producing
means then synthesizes a first picture signal based on the first
image signal with a second picture signal based on the second image
signal. The dynamic range for an image signal can be expanded, and
it can be prevented that the signal-to-noise ratio of a signal
component indicating a low luminance level deteriorates. Moreover,
a picture signal whose input/output characteristic changes smoothly
and which renders a natural image not giving any sense of
incongruity can be produced.
In the aforesaid embodiments, a first image signal represents a
first image projected during a long exposure time and a second
image signal represents a second image projected during a short
exposure time. The first image signal and second image signal are
weighted with two weight coefficients f and g that are determined
relative to brightness levels ranging up to a brightness level at
which the second image signal has a saturation value. The resultant
image signals are added up, thus producing a synthetic picture
signal representing a synthetic image.
Alternatively, when a brightness level is higher than the
brightness level at which the first image signal has a saturation
value, a weight coefficient G specified with the level of the
second image signal may be used to produce the output M having the
characteristic like the one expressed with the curve in FIG. 5.
Even in this case, the same configuration as the first embodiment
is adopted. However, data stored in the first LUT 25 and second LUT
26 is different from that shown in FIG. 2.
For example, as long as a brightness level ranges from 0 to ys1, an
output M1 is identical to that in the first embodiment. The output
M1 corresponding to a synthetic picture signal is expressed as
follows:
When the brightness level y is equal to or larger than ys1, an
output M2 is provided as follows:
In this case, a boundary condition for the output M2 is defined as
follows:
Namely, the derived functions of M1 and M2 relative to the
brightness level y that is ys1 are equal to each other.
Thus, the output M1 joins smoothly with the output M2 at the
brightness level ys1. Moreover, the output M2 relative to the
brightness level ys2 is defined as follows:
The output M2 is, as shown in FIG. 10, characterized to vary
smoothly relative to brightness levels ranging from ys1 to ys2.
In this case, from the first LUT 25, a weight coefficient cos.sup.2
(px2) is read based on the image signal x2 relative to brightness
levels ranging from 0 to ys1. A weight coefficient 0 is read
relative to a brightness level exceeding ys1.
Moreover, from the second LUT 26, a weight coefficient sin.sup.2
(px2) is read based on the image signal x2 relative to brightness
levels ranging from 0 to ys1. When the brightness level exceeds
ys1, the weight coefficient is set to a value satisfying the
aforesaid condition.
FIG. 10 graphically shows a characteristic of an output M', which
is a synthetic picture signal in this case, relative to a
brightness level y. The characteristic is fundamentally identical
to that shown in FIG. 5. That is to say, as described above, when
the brightness level of an object is equal to or higher than a
brightness level at which the first image signal has a saturation
value, a synthetic picture signal is characterized by the weight
coefficient G specified by the second image signal.
In the example shown in FIG. 10, the weight coefficient G decreases
monotonously relative to the brightness level y. The weight
coefficient G associated with the brightness level ys1 is given as
G(ys1)>1. The weight coefficient G associated with the
brightness level ys2 is given as G(ys2)=1.
Even in this variant, almost the same advantages as those of the
first embodiment are provided.
As described above with reference to, for example, FIG. 1, the
dynamic range expanding circuits 15R, 15G, and 15B are arranged on
the output stage of the knee and gamma circuit 12. The dynamic
range expanding circuits 15R, 15G, and 15B may be designed to have
the capability of the knee and gamma circuit 12.
Moreover, the dynamic range expanding circuit 40 in FIG. 6 may be
designed to have the capability of an amplifier for amplifying an
output of the CCD 2. Herein, the output is amplified so that the
saturation value of the output level will be equal to that of a
picture signal output to the monitor 19. In this case, the sum of
the weight coefficients f and g may be set to a given value larger
than 1. The saturation value of an output level of the dynamic
range expanding circuit 40 will then be equalized to that of a
picture signal output to the monitor 19.
Third Embodiment
The third embodiment adopting the aforesaid first and second
embodiments (including the variant) will be described below.
Briefly, the third embodiment includes a brightness detecting
means. A weight coefficient characterizing a synthetic picture
signal is selected based on a signal output from the brightness
detecting means. Otherwise, the weight coefficient can be selected
manually.
The fourth embodiment adopts a progressive CCD having two
horizontal transfer output circuits as an imaging device.
The fifth embodiment is adapted to an endoscopic imaging apparatus.
In this embodiment, an exit pupil is divided into two portions. Two
imaging devices are employed. A wide dynamic range is offered, and
an image suitable for endoscopic diagnosis can be constructed.
According to the sixth, seventh, and eighth embodiments, the
waveform of an output signal of an imaging device is detected.
Based on the waveform, one of two different exposure times or the
other thereof or both thereof are changed.
The ninth to thirteenth embodiments are endoscopic imaging
apparatuses. A filter member is located in front of an imaging
device. An amount of light incident on the imaging device is thus
controlled to produce two images similar to images projected during
different exposure times. Otherwise, field-sequential color imaging
may be carried out under field-sequential illumination. An amount
of illumination light used to illuminate an object may be
controlled using an illuminating means, whereby two images similar
to those projected during different exposure times are
constructed.
Next, the third embodiment of the present invention will be
described with reference to FIGS. 11 to 17. An imaging apparatus 51
shown in FIG. 11 includes an imaging unit 52, a signal processing
unit 53, and a monitor 54. Specifically, the imaging unit 52 is
responsible for imaging. The signal processing unit 53 processes a
signal output from the imaging unit 52. The monitor 54 displays an
image according to a video signal produced by the signal processing
unit 53.
The imaging unit 52 includes an imaging lens 55 for forming an
object image, and a CCD 56 serving as a solid-state imaging device
located on the image plane of the imaging lens 55. The CCD 56 is a
CCD having, for example, a photoelectric converter and transferring
device. A mosaic filter for optically separating color signal
components is located in front of the photoelectric converter.
The signal processing unit 53 includes a reference signal
generating circuit (abbreviated to SSG) 57 for generating a
reference signal. The reference signal generated by the SSG 57 is
output to a first timing signal generating circuit 58 and a second
timing signal generating circuit 59. A timing signal generated by
the first timing signal generating circuit 58 is applied to a CCD
driver 60. The CCD driver 60 applies a CCD driving signal to the
CCD 56 synchronously with the timing signal.
The CCD driver 60 outputs two CCD driving signals during one frame
period (for example, 1/30 sec). With the CCD driving signals, two
image signals produced during different exposure times are output.
One of the two image signals produced during one frame period,
which renders one field (however, a frame image), is produced at a
high shutter speed equivalent to a short exposure time (for
example, 1/150 sec). The other image signal rendering the other
field is produced at a low shutter speed equivalent to a long
exposure time (for example, four times longer than the exposure
time equivalent to the high shutter speed, that is, 1/37.5 sec).
The sum of the two exposure times is 1/30 sec corresponding to one
ordinary frame period during which a standard video signal is
scanned.
The image signal (charge) produced at the high shutter speed and
the image signal (charge) produced at the low shutter speed are
read alternately from the CCD synchronously with a vertical sync
signal (abbreviated to VD) during one field period.
An image signal is photoelectrically converted by the CCD 56, and
then output from the (transferring device) CCD 56 to a preamplifier
61. After amplified, the image signal is input to a correlative
double sampling (CDS) circuit 62. A reset noise and others are
removed and signal components are extracted. The resultant signal
is input to an A/D converting circuit 63 and brightness sensing
circuit 64.
The A/D converting circuit 63 converts an analog signal into a
digital signal. The digital signal is input to a dynamic range
expanding circuit (D range expanding circuit in FIG. 11) for
expanding a dynamic range. A selection signal output from the
brightness sensing circuit 64 is also input to the dynamic range
expanding circuit 65.
The brightness sensing circuit 64 detects a maximum luminance level
indicated by the image signal produced at the high shutter speed.
Based on the maximum luminance level, the brightness sensing
circuit 64 produces a selection signal assisting in selecting a
function used to expand a dynamic range by the dynamic range
expanding circuit 65.
For example, depending on whether the maximum luminance level
exceeds a reference value, a selection signal indicating either of
dynamic range expansion modes is output. In one of the modes, the
dynamic range for an image signal is expanded so that the image
signal will exhibit a characteristic that even a signal component
indicating a high luminance level does not have a saturation value.
In the other mode, the dynamic range for an image signal is
expanded so that the image signal exhibits a characteristic that a
signal component indicating a lower luminance level does not have
the saturation value.
The brightness sensing circuit 64 is composed of a peak value
detecting circuit 64A for detecting a peak value and a comparing
circuit 64B. The maximum luminance level can therefore be detected
by the peak value detecting circuit 64A. An output of the peak
value detecting circuit 64A is compared with a reference value Vref
by the comparing circuit 64B. An output signal of the comparing
circuit 64B is input as the selection signal to the dynamic range
expanding circuit 65.
A signal for which dynamic range has been expanded by the dynamic
range expanding circuit 65 is input to a processing circuit 66.
Color signal components are then separated and converted into red,
green, and blue signals. The white balance detected in each of the
red, green, and blue signals is adjusted. The resultant signals are
then input to a contour enhancing circuit 67.
The contour enhancing circuit 67 enhances the red, green, and blue
signals in terms of the contour of an image. The resultant red,
green, and blue signals are input to and stored temporarily in a
memory 68. Signals read from the memory 68 are input to a D/A
converting circuit 69, and then converted into analog red, green,
and blue signals. The red, green, and blue signals are input to a
monitor 54. An object image is displayed in colors on a monitor
screen.
An output signal of the second timing generating circuit 59 is
input to the dynamic range expanding circuit 65, processing circuit
66, contour enhancing circuit 67, and memory 68.
FIG. 12 shows a configuration of the dynamic range enhancing
circuit 65. A digital image signal sent from the A/D converting
circuit 64 is temporarily stored in a memory 71 having a storage
capacity corresponding to the number of all pixels permitted by the
CCD 56. The image signal is then input to a first look-up table
(LUT) 73A and second LUT 73B via selectors 72A and 72B which are
switched according to a field judgment signal sent from the second
timing signal generating circuit 59.
Moreover, a signal read from the memory 71 is input to the first
LUT 73A and second LUT 73B via the selectors 72A and 72B. A
selection signal produced by sensing a brightness level by the
brightness sensing circuit 65 is input to the first LUT 73A and
second LUT 73B. Based on the selection signal, a synthesis function
actually employed is selected from among a plurality of synthesis
functions that are stored in the first LUT 73A and second LUT 73B
and used to expand a dynamic range.
Signals read from the first LUT 73A and second LUT 73B are input to
an adding circuit 74, and then to an interpolating circuit 75.
After interpolated, a resultant signal is provided as an output
signal of the dynamic range expanding circuit 65, and input to the
processing circuit 66 on the succeeding stage. Color signal
components are then separated.
FIG. 13 is a graph showing curves expressing different input/output
characteristics represented by synthesis functions one of which is
selected with a selection signal output from the brightness sensing
circuit 64 in order to expand a dynamic range.
When an object is image at a low shutter speed, an output of the
CCD exhibits a characteristic S1 of increasing along a straight
line, which has a large slope, relative to an amount of incident
light. Once the output has a level of a saturation value Csat, the
output remains constant. By contrast, when the object is imaged at
a high shutter speed, the CCD output exhibits a characteristic Ss
of increasing along a straight line, which has a small slope,
relative to an amount of incident light.
Image data items produced to exhibit the characteristics S1 and Ss
are weighted through the first LUT 73A and second LUT 73B, whereby
a dynamic range can be expanded. In this embodiment, a selection
signal is used to select a function used to expand a dynamic range.
Two characteristic functions S1 and Ss are synthesized by assigning
them to the selected function. Consequently, the dynamic range for
a signal can be expanded so that the signal will exhibit either of
input/output characteristics A and B drawn with a dot-dash line and
alternate long and two short dashes line respectively.
For example, when a maximum luminance level detected in a signal is
high, the dynamic range for the signal is expanded so that the
signal will exhibit characteristic B. Specifically, a signal
component indicating a low luminance level will be suppressed. A
signal component indicating a high luminance level will not have a
saturation value, and a variation of the signal component will be
reflected in an image displayed. When the maximum luminance level
detected in a signal is low, the dynamic range for the signal is
expanded so that the signal will exhibit characteristic A.
Specifically, a signal component indicating a high luminance level
will be suppressed, and a variation of a signal component
indicating a low luminance level will be reflected in an image
displayed.
In this embodiment, the first LUT 73A and second LUT 73B store a
plurality of synthesis functions used to expand a dynamic range.
FIG. 14 shows data of the functions stored in the first LUT 73A and
second LUT 73B respectively.
The first LUT 73A and second LUT 73B have addresses each having a
length of, for example, 9 bits. Functions F0 and G0 are allocated
to lower 8-bit addresses 000 to 0FF, and functions F1 and G1 are
allocated to upper 8-bit addresses 100 to 1FF.
A signal passed by the A/D converting circuit 63 or a signal read
from the memory 71 is applied to the lower 8-bit address terminals.
A selection signal sent from the brightness sensing circuit 64 is
applied to the uppermost address terminal. Based on the selection
signal, any of a plurality of functions used to expand a dynamic
range is selected.
For example, when the selection signal is low or 0, data of the
function F0 or G0 is read out. In this case, a resultant signal
exhibits the characteristic A shown in FIG. 3. When the selection
signal is high or 1, data of the function F1 or G1 is read out. In
this case, the resultant signal exhibits the characteristic B shown
in FIG. 13.
Next, the actions of this embodiment will be described with
reference to the timing charts of FIGS. 15A to 15K.
As shown in FIG. 15A, the CCD driver 60 applies signal readout
pulses RSI and RLI shown in FIG. 15B to the CCD 56 at the starts of
a short exposure time SI and long exposure time LI (I=1, 2, etc.).
Charge of a signal photoelectrically converted by the photoelectric
converter of the CCD 56 and then stored is transferred to the
transfer device of the CCD 56.
When the signal charge transferred to the transfer device has been
produced during the short exposure time SI, the read transferred
signal is applied synchronously with a vertical sync signal VD
shown in FIG. 15D during one field period. The signal is stored as
a CCD output CSI shown in FIG. 15C in the memory 71 as shown in
FIG. 15F, and applied to the second LUT 73A via the selector
72A.
When the signal charge transferred to the transfer device has been
produced during the long exposure time LI, the read transferred
signal is applied synchronously with the vertical sync signal VD
immediately succeeding the signal read pulse RL1 during one field
period. The signal is stored as a CCD output CLI shown in FIG. 15C
in the memory 71 as shown in FIG. 15F, and applied to the second
LUT 73B via the selector 73B.
The selectors 72A and 72B are switched with a field judgment
signal, which is shown in FIG. 15E, output from the second timing
signal generating circuit 59. For example, when the field judgment
signal is high, a node a shown in FIG. 12 is selected. The CCD
output CSI is input to the first LUT 73A. A signal produced during
the previous frame period and stored in the memory 71, that is, a
CCD output CLI-1 is input to the second LUT 73B.
Moreover, when the field judgment signal is low, a node b is
selected. The CCD output CSI read from the memory 71 is input to
the first LUT 73A, and the CCD output CLI is input to the second
LUT 73B.
For brevity's sake, outputs of the selectors 72A and 72B are
illustrated to be input to the first LUT 73A and second LUT 73B
respectively as indicated with solid lines. Alternatively, they may
be input to the first LUT 73A and second LUT 73B as indicated with
dashed lines in FIG. 12.
In this case, the functions F0 and G0 are F0(SI, LI) and G0(SI,
LI), thus expressing the characteristics of image signals produced
during the short exposure time SI and long exposure time LI.
When two signals are input to each of the first LUT 73A and second
LUT 73B, synthesis can be achieved more finely.
For inputting two signals, since the number of bits is very large,
some high-order bits of the signals may be input. In this case, a
ROM whose storage capacity is not very large may be used as the
first LUT 73 and second LUT 73B.
For example, when the selection signal is, as shown in FIG. 15K,
low, the function F0 is selected from the first LUT 73A as shown in
FIG. 15H. Moreover, the function G0 is selected from the second LUT
73B as shown in FIG. 15I. In this case, the functions are added up
by the adding circuit 74. An additive output H shown in FIG. 15J,
that is, a mixed function H is therefore F0+G0. The dynamic range
for a signal is expanded so that the signal will exhibit the
characteristic A shown in FIG. 13.
When the selection signal is high, the function F1 in the first LUT
73A is selected for use. The function G1 in the second LUT 73B is
selected for use. In this case, the functions are added up by the
adding circuit 74. The mixed function H becomes F1+G1. The dynamic
range for a signal is expanded so that the signal will exhibit the
characteristic B shown in FIG. 13.
As mentioned above, when the maximum brightness level of an object
is high, or in other words, when the maximum luminance level
detected in an image signal is high, the dynamic range for an image
signal is expanded so that the signal will be characterized by a
signal component indicating a high luminance level. Specifically,
the signal component indicating a high luminance level reflects a
change in brightness of the object. When the maximum luminance
level is low, the dynamic range for a signal is expanded so that
the signal will be characterized by a signal component indicating a
low luminance level. Specifically, the signal component indicating
a low luminance level reflects a change in brightness of the
object.
According to this embodiment, the dynamic range for a signal can be
expanded so that the signal will exhibit a characteristic suitable
for an actual use environment (or imaging environment).
FIG. 16 shows a configuration of a dynamic range expanding circuit
65' in a variant of the third embodiment.
According to this variant, a selection signal and selection
instruction signal are input to the first LUT 73A and second LUT
73B, which are included in the dynamic range expanding circuit 65
shown in FIG. 12, via a selector 78. Herein, the selection signal
is sent from the brightness sensing circuit 64 and the selection
instruction signal is sent from a selection switch 77 handled
manually by a user.
The selector 78 can be handled manually. The selector 78 may be set
to a state in which the selection signal sent from the brightness
sensing circuit 64 is selected. Alternatively, the selector 78 may
be set to a state in which the selection instruction signal sent
from the selection switch 77 that can be handled by a user is
selected.
In this variant, a first LUT 73A' and second LUT 73B' contain
numerous functions F0, F1, F2, etc. and G0, G1, G2, etc. An
actually used function is selected from among the numerous
functions F0, F1, F2, etc., and G0, G1, G2, etc.
By selecting any of the functions, the dynamic range for a signal
can be expanded so that the signal will exhibit any of the
different characteristics A, B, C, and D shown in FIG. 17.
In this variant, three or more functions (or three or more sets of
functions) can be selected. The selection signal is therefore a
digital signal of two or more bits long. In this case, the
brightness sensing circuit 64 detects a maximum luminance level and
minimum luminance level in an image signal produced at a high
shutter speed. The selection signal to be produced indicates
whether the maximum luminance level and minimum luminance level are
equal to or higher than reference values.
A function is selected as described below. For example, when the
maximum luminance level is high, the dynamic range for a signal
will be expanded by putting emphasis on a signal component
indicating a high luminance level. When the maximum luminance level
is low, the dynamic range for a signal will be expanded by putting
emphasis on a signal component indicating a low luminance level.
When the minimum luminance level is high, the signal component
indicating a low luminance level will be suppressed. On the
contrary, when the minimum luminance level is low, the dynamic
range for a signal will be expanded so that a signal component
indicating a low luminance level will not be suppressed.
To be more specific, assume that the maximum luminance level
detected in a signal is high and the minimum luminance level
detected therein is low. In this case, the dynamic range for the
signal is expanded by putting emphasis on signal components
indicating high and low luminance levels. In other words, the
dynamic range for the signal is expanded so that the signal will
exhibit the characteristic D shown in FIG. 17. Namely, a signal
component indicting an intermediate luminance level will be
suppressed and the signal components indicating high and low
luminance levels will be emphasized.
Moreover, assume that the maximum luminance level detected in a
signal is low and the minimum luminance level detected therein is
low. In this case, the dynamic range for the signal is expanded so
that a signal component indicating a high luminance level will be
suppressed and a signal component indicating a low luminance level
will be emphasized. In other words, the dynamic range for the
signal is expanded so that the signal will exhibit the
characteristic A shown in FIG. 17. Namely, the signal component
indicating a high luminance level will be suppressed and the signal
component indicating a low luminance level will be emphasized.
The other components are identical to those of the first
embodiment. According to this variant, the dynamic range for a
signal can be expanded using a mixed function suitable for a
brightness level of an object sensed by the brightness sensing
circuit 64.
Moreover, a user can expand the dynamic range for a signal so that
the signal will exhibit a characteristic different from a
characteristic selected by sensing a brightness level. That is to
say, a signal component extracted from a different viewpoint will
be able to be emphasized.
For example, assume that a change in luminance in a normal image
must be observed by putting emphasis on, especially, a dark
portion. In this case, the characteristic function C shown in FIG.
17 is selected. Consequently, the dynamic range for a signal is
expanded so that a change in luminance indicated by a signal
component indicating a low luminance level will be reflected and a
signal component indicating a high luminance level will be
suppressed.
Fourth Embodiment
Next, the fourth embodiment of the present invention will be
described with reference to FIGS. 18 to 22.
An imaging apparatus 80 shown in FIG. 18 consists of a camera head
81, a camera control unit (hereinafter, CCU) 82, and a TV monitor
83. Specifically, the CCU 82 controls the camera head 81 and
processes an output of the camera head. The TV monitor 83 is an
interlacing type display for displaying an image whose data has
been processed by the CCU 82. The camera head 81 is mounted on an
eyepiece unit of, for example, a rigid endoscope.
The camera head 81 includes a CCD 85 that is a progressive scanning
type imaging device (hereinafter, progressive CCD). The progressive
CCD 85 photoelectrically converts an object image formed on the
image plane of an image formation lens that is not shown, and
outputting an analog image signal. The progressive CCD 85 has two
output systems; that is, a first output system for providing a
first CCD output 85a and a second output system for providing a
second CCD output 85b.
An output of the camera head 81, that is, the first CCD output 85a
and second CCD output 85b are routed to the CCU 82 over signal
cables that are not shown.
The CCU 82 includes CDS/AGC circuits 86a and 86b, A/D converting
circuits 87a and 87b, LUTs 88a and 88b, an adder 89, a switching
means 90, a digital signal processing (DSP) circuit 91, a D/A
converting circuit 92, a timing generator (TG) 93, and a sync
signal generating circuit (SSG) 94. Specifically, the CDS/AGC
circuits 86a and 86b amplify the first CCD output 85a and second
CCD output 85 (control gains autonomously), and carry out
correlative double sampling and others. The A/D converting circuits
87a and 87b convert outputs of the CDS/AGC circuits 86a and 86b
into digital signals. The LUT 88a and 88b are referenced in order
to convert data nonlinearly according to the outputs of the A/D
converting circuits 87a and 87b, and output resultant data. The
adder 89 adds up outputs of the LUTs 88a and 88b. The switching
means 90 selects an output of the adder 89 in a wide dynamic range
mode. In a normal mode, the switching means 90 selects an output of
the A/D converting circuit 87a. The DSP circuit 91 digitally
processes an output of the switching means 90. The D/A converting
circuit 92 converts a digitized signal into an analog signal. The
TG 93 supplies a driving pulsating signal to the progressive CCD 85
and CDS/AGC circuits 86a and 86b. The SSG 94 supplies a reference
signal to the TG 93, A/D converting circuits 87a and 87b, and DSP
91.
The LUTs 88a and 88b and the adder 89 constitute a dynamic range
expanding means.
An output of the D/A converting circuit 92 is output to the TV
monitor 83 connected over a signal cable that is not shown. An
operator handles the rigid endoscope in various manners while
viewing the TV monitor 83.
Next, a configuration of the progressive CCD 85 will be described
with reference to FIG. 19. For brevity's sake, only a small number
of pixels are shown in FIG. 19. In reality, the progressive CCD
includes a larger number of pixel locations.
The progressive CCD 85 consists of a plurality of photodiodes 96,
vertical shift registers 97, and two systems of horizontal shift
registers 98a and 98b. Specifically, the plurality of photodiodes
96 is arranged two-dimensionally. The vertical shift registers 97
transfer charges accumulated in the photodiodes 96 in a vertical
direction. The two systems of horizontal shift registers 98a and
98b transfer charges, which are sent from the vertical shift
registers 97, in a horizontal direction. Outputs of the horizontal
shift registers 98a and 98b are the first CCD output 85a and second
CCD output 85b.
Readout by the progressive CCD 85 will be described with reference
to FIGS. 19, 20, and 21.
To begin with, readout in a wide dynamic range mode will be
described.
Charge is accumulated in the photodiodes 96. At this time, control
is given so that a charge accumulation time will be different
between odd lines ODD1, ODD2, ODD3, etc. and even lines EVEN1,
EVEN2, etc. In other words, for example, a high shutter speed of
1/240 sec is set as the charge accumulation time for the odd lines.
A low shutter speed of 1/60 sec (=4/240 sec) is set as the charge
accumulation time for the even lines. Charge is swept away from the
odd lines during 3/240 sec within the charge accumulation time 1/60
sec within which charge is accumulated on the even lines. Charge is
accumulated on the odd lines during the remaining 1/240 sec.
The charges thus accumulated in the photodiodes 96 are transferred
all together to the vertical shift registers 97. Thereafter, the
vertical shift registers 97 shift charges constituting two lines in
the vertical direction. Consequently, the charges on the even line
EVEN1 are transferred to the horizontal shift register 98b. The
charges on the odd line ODD1 are transferred to the second
horizontal shift register 98b. This causes the horizontal shift
registers 98a and 98b to quickly shift data items constituting one
line in the horizontal direction.
Thereafter, the vertical shift registers 97 shift charges
constituting two lines in the vertical direction. The charges on
the even line EVEN2 are then transferred to the first horizontal
shift register 98a. The charges on the odd line ODD2 are
transferred to the second horizontal shift register 98b. Similarly,
the horizontal shift registers 98a and 98b shift charges in the
horizontal direction. These operations are repeated.
When the charges in all the photodiodes 96 have been transferred,
charge transfer for one field is completed. For this field, the
first horizontal shift register 98a outputs an image signal
produced at the low shutter speed to represent the even lines. The
second horizontal shift register 98b outputs an image signal
produced at the high shutter speed to represent the odd lines.
Whether the field is regarded as an even field or odd field can be
determined appropriately. Since the output of the first shift
register 98a represents the even lines, the field shall be regarded
as an even field.
Thereafter, for reading data that renders an odd field, a
combination of lines from which charges are transferred to the
horizontal shift registers 98a and 98b is changed.
First, charge is accumulated during a time that is different
between the odd lines and even lines. At this time, the shutter
speeds at which the odd lines and even lines are formed are
opposite to those for rendering the even field. For example, the
odd lines are formed at the low shutter speed of 1/60 sec and the
even lines are formed at the high shutter speed of 1/240 sec.
Charges thus accumulated in the photodiodes 96 are transferred
simultaneously to the vertical shift registers 97. Thereafter, the
vertical shift registers 97 shift charges constituting one line in
the vertical direction. Charges constituting the odd line ODD1 are
then transferred to the first horizontal shift register 98a. The
first horizontal shift register 98a shifts the charges in the
horizontal direction quickly.
Thereafter, the vertical shift registers 97 transfer charges
constituting two lines in the vertical direction. Charges
constituting the odd line ODD2 are therefore transferred to the
first horizontal shift register 98a. Charges constituting the even
line EVEN1 are transferred to the second horizontal shift register
98b. The horizontal shift registers 98a and 98b each quickly
transfer data items constituting one line in the horizontal
direction. Thereafter, the vertical shift registers 97 transfer
charges constituting two lines successively. The horizontal shift
registers 98a and 98b output the charges in due course.
When the charges in all the photodiodes 96 have been transferred,
transfer of charges for rendering the odd field is completed. For
the odd field, an image signal produced at the low shutter speed to
represent the odd lines is output from the first horizontal shift
register 98a. An image signal produced at the high shutter speed to
represent the even lines is output from the second horizontal shift
register 98b.
The output of the first horizontal shift register 98a that is an
image signal produced at the low shutter speed is the first CCD
output 85a. The output of the second horizontal shift register 98b
that is an image signal produced at the high shutter speed is the
second CCD output 85b.
As shown in FIG. 20, during an odd field period within one frame
period of 1/30 sec, the data representing the odd lines (ODD) is
output as the first CCD output 85a. The data representing the even
lines (EVEN) is also output as the second CCD output 85b. During a
subsequent even field period, the data representing the even lines
(EVEN) is output as the first CCD output 85a, and the data
representing the odd lines (ODD) is output as the second CCD output
85b. Large dynamic range processing to be performed based on the
data items will be described later.
Next, readout in the normal mode will be described.
In the normal mode, the charge accumulation time during which
charge is accumulated in the photodiodes 96 is the same between the
even lines and odd lines.
Charges thus accumulated are transferred simultaneously from the
photodiodes 96 to the vertical shift registers 97. Thereafter, the
vertical shift registers 97 shift charges constituting one line in
the vertical direction. Charges constituting the odd line ODD1 are
therefore transferred to the first horizontal shift register 98a.
Thereafter, the vertical shift registers 97 shift charges
constituting one line in the vertical direction. At this time, the
potential at the second horizontal shift register 98b is, for
example, high to prevent the charges from being transferred to the
second horizontal shift register 98b. The data representing the odd
line ODD1 and the data representing the even line EVEN1 are added
up in the first horizontal shift register 98a. The horizontal shift
register 98a then quickly shifts the resultant data in the
horizontal direction.
Likewise, the vertical shift registers 97 shift charges
constituting two lines in the vertical direction. The data
representing the odd line ODD2 and the data representing the even
line EVEN2 are added up in the horizontal shift register 98a. The
similar operations are then repeated.
For reading data that renders a subsequent field, a combination of
lines whose data items are to be added up is changed.
Specifically, as mentioned above, charge is accumulated during a
time that is the same between the odd lines and even lines. Charges
accumulated in the photodiodes 96 are then transferred
simultaneously to the vertical shift registers 97. Thereafter, the
vertical shift registers 97 transfer charges constituting one line
(data of the odd line ODD1) in the vertical direction. The first
horizontal shift register 98a quickly shifts the charges in the
horizontal direction.
Thereafter, the vertical shift registers 97 shift charges
constituting two lines in the vertical direction. The data of the
even line EVEN1 and the data of the odd line ODD2 are added up in
the horizontal shift register 98a. The horizontal shift register
98a then shifts the resultant data in the horizontal direction and
thus outputs it. The addition and output will be carried out in the
same manner thereafter.
As mentioned above, the foregoing data items rendering two fields
are, as shown in FIG. 21, output successively as odd-field (ODD)
data and even-field (EVEN) data from the first CCD output unit
85a.
Now, how image data output from the progressive CCD is processed by
the CCU 82 will be described below.
To begin with, processing in the wide dynamic range mode will be
described. In this mode, the switching means 90 is changed over to
the adder 89.
The first CCD output 85a and second CCD output 85b are amplified by
the CDS/AGC circuits 86a and 86b respectively. Correlative double
sampling and others are carried out. Outputs of the CDS/AGC
circuits 86a and 86b are converted into digital signals by the A/D
converting circuits 87a and 87b. The outputs are then converted by
referencing the LUTs 88a and 88b. The converted outputs are then
added up by the adder 89 on the succeeding stage, and then
converted into given data items as outputs having undergone wide
dynamic range processing.
The wide dynamic range processing will be described with reference
to FIG. 22.
FIG. 22 shows relationships between the brightness level of an
object and the levels of image signals produced at different
shutter speeds (charge accumulation times).
When an object is imaged at a low shutter speed (LS), it means that
a charge accumulation time is long. A dark portion of the object
can be imaged more accurately. However, a portion of the object
whose brightness level is so high as to exceed Bs in FIG. 22 cannot
be imaged properly. This is because a corresponding signal
component output from an imaging device has a saturation value as a
level Vs.
On the other hand, when an object is imaged at a high shutter speed
(HS), an amount of light accumulated in the photodiodes 96 in the
progressive CCD 85 is reduced. The CCD output is therefore plotted
as a straight line HS, which is inclined smoothly, in FIG. 22. Even
when an object whose brightness level exceeds Bs is imaged, a
produced image signal will not have the saturation value.
Thus, when an object is imaged at a low shutter speed, a portion of
the object whose brightness level may be so high that the CCD is
saturated. In this case, the corresponding portion of the object
image is compensated using an image produced at a high shutter
speed. This results in an image in which a dark portion of the
object is not seen blackened and the high-brightness level portion
is not seen streakily whitened. In other words, a picture signal
(whose data is plotted as a curve HD in FIG. 22) proving a wide
dynamic range can be produced.
Assume that the data of the first CCD output 85a produced at the
low shutter speed is x and the data of the second CCD output 85b
produced at the high shutter speed is y. Data processed to expand a
dynamic range, z, is expressed by the following equation 1:
where functions f and g are defined in consideration of the output
characteristic of the progressive CCD 85.
The dynamic range expansion processing is generally nonlinear
processing. If an arithmetic operation were carried out at every
imaging, the load of the arithmetic operation would increase and
the processing time would extend.
Data to be involved in the arithmetic operation of the above
equation is therefore stored in advance in tables, that is, the
LUTs 88a and 88b. In practice, the LUTs are referenced to draw out
a result.
Odd (even) line data and even (odd) line data, which render the
same field, are converted into relevant data items by referencing
the LUTs 88a and 88b. Herein, the odd line data is the first CCD
output 85a produced at the low shutter speed, and the even line
data is the second CCD output 85b produced at the high shutter
speed. The data items are added up by the adder 89. Thus, a dynamic
range is optimized.
A video output signal processed to optimize a dynamic range is
plotted as shown in the uppermost row in FIG. 20. OE denotes data
rendering an odd field, wherein data representing even lines is
added to the data. EO denotes data rendering an even field, wherein
data representing odd lines is added to the data.
As illustrated, data processed to optimize a dynamic range is an
ordinary interlacing video output signal. A signal output via the
DSP 91 and D/A converting circuit 92 can therefore be output to the
ordinary TV monitor 83 as it is.
Next, the normal mode will be described. In this mode, the
switching means 90 is changed over to the A/D converting circuit
87a.
As mentioned above, in the normal mode, the interlacing signal
shown in FIG. 21 is produced based on the first CCD output 85a
alone. The signal is output to the ordinary TV monitor 83 via the
CDS/AGC circuit 86a, A/D converting circuit 87a, switching means
90, DSP 91, and D/A converting circuit 92 as it is.
According to this embodiment, a progressive CCD is employed. A
first CCD output and second CCD output produced at different
shutter speeds are processed nonlinearly and added up. Thus, data
processed to realize a wide dynamic range can be produce during one
field period (1/60 sec). A vertical resolution will therefore not
deteriorate.
Moreover, the same progressive CCD may be read in different modes.
A video output signal for a wide dynamic range mode or a video
output signal for a normal mode can be produced merely by switching
a switch.
Furthermore, a video output signal produced by realizing a wide
dynamic range is conformable to the interlacing. A TV monitor can
be used for display in common between the wide dynamic range mode
and normal mode advantageously obviating the necessity of preparing
any special monitor.
The present invention is not limited to the mode presented by this
embodiment. Needless to say, various variations and applications
can be constructed without a departure from the gist of the
embodiment.
As described so far, according to this embodiment, an imaging
apparatus whose vertical resolution will not be deteriorated can be
realized.
Fifth Embodiment
Next, the fifth embodiment of the present invention will be
described with reference to FIGS. 23 to 25. As shown in FIG. 23, an
endoscopic imaging apparatus 101 of this embodiment consists of a
camera head 102, a scope 103, a light source unit 104, a CCU 105,
and a TV monitor 106. Specifically, the camera head 102 has an
imaging means incorporated therein. The scope 103 is connected to
the camera head 102. The light source unit 104 supplies
illumination light to the scope 103. The CCU 105 processes a signal
sent from the imaging means incorporated in the camera head 102.
The TV monitor 106 displays an image according to a standard video
signal processed by the CCU 105.
An objective 110 is located at the tip of the scope 103. A single
system of relay lenses 111 extending from the back of the objective
110 to the camera head 102 is incorporated in the scope 103. An
object image formed by the objective 110 is propagated by the
system of relay lenses 111 and input to the imaging means in the
camera head 102. Moreover, an illumination light guide 107 used to
illuminate an object with illumination light is running through the
scope 103.
When the endoscopic imaging apparatus 101 is in use, the light
guide 107 running through the scope 103 is, as shown in FIG. 23,
coupled to the light source unit 104. Illumination light emanating
from a lamp 104 in the light source unit 104 then passes through an
aperture stop 104b. The illumination light is then converged by a
lens 104c, and routed to the end surface of the light guide 107
opposed to the lens 104c.
The illumination light is propagated to the scope 103 by way of the
light guide 107, passed through the scope 103, and emitted forward
through the distal side of the scope 103. An object such as a
patient's body cavity is thus illuminated. Light reflected from the
illuminated object is converged by the scope 103. An object image
is then propagated by the objective 110 and system of relay lenses
111 in the scope 103, and projected by the imaging means in the
camera head 102.
In the camera head 102, a pupil divider 112 is located behind the
sole system of relay lenses 111. The object image propagated by the
system of relay lenses 111 is divided into a plurality of images,
or in this embodiment, two images. An image formation optical
system 113 is located behind the pupil divider 112, thus facing two
images provided by the pupil divider 112. First and second
solid-state imaging devices 114 and 115 to be opposed to the two
images are located behind the image formation optical system
113.
In this embodiment, a CCD is adopted as the solid-state imaging
device. The first and second solid-state imaging devices 114 and
115 will therefore be referred to as the first and second CCDs 114
and 115. Object images produced by bisecting the object image by
means of the pupil divider 112 are formed on the image planes of
the first CCD 114 and second CCD 115 respectively. The object
images are then photoelectrically converted.
CCD driving signals for driving the first CCD 114 and second CCD
115 are transmitted over two systems of CCD driving signal
transmission lines. CCD output signals output from the CCDs are
transmitted over two systems of CCD output signal transmission
lines. The transmission lines are contained in a camera cable 108,
and coupled to the CCU 105 via a camera connector 109. The output
signals of the CCDs 114 and 115 are sent to the CCU 105 and
subjected to various kinds of signal processing. A video signal
output from the CCU 105 is sent to the TV monitor 106. A view image
of an object is then displayed on the TV monitor 106.
In the CCU 105, a first CCD drive circuit 121 and second CCD drive
circuit 129 are incorporated as circuits for driving the first CCD
114 and second CCD 115 respectively. The CCD drive circuits 121 and
129 supply CCD driving signals to the CCDs 114 and 115 respectively
over the CCD driving signal transmission lines in the camera cable
108. Charges of signals accumulated in the CCDs 114 and 115 are
then read out.
Moreover, two signal processing systems are installed in the CCU
105 in order to handle the output signals of the first CCD 114 and
second CCD 115 respectively. To begin with, a processing system for
handling the output signal of the first CCD 114 will be
described.
A preamplifier 124 is installed on an initial stage of the CCU 105.
The transmission line over which the output signal of the first CCD
114 is transmitted is coupled to the preamplifier 124. A CCD output
signal read from the CCD 114 is transmitted to the CCU 105 over the
CCD output transmission line in the camera cable 108. A loss
occurring during cable transmission is amplified by the
preamplifier 124, whereby given processing is carried out.
On the stage succeeding the preamplifier 124, a CDS circuit and
sample-and-hold circuit that are not shown are installed. The CCD
output signal amplified by the preamplifier 124 is pre-processed by
the CDS (correlative double sampling) circuit and sample-and-hole
circuit.
On the stage succeeding these circuits, there are an A/D converting
circuit 125 and digital signal processing circuit (DSP) 126. After
the CCD output signal undergoes the above given pre-processing, it
is input to the A/D converting circuit 125 and then converted into
a digital signal. Given digital signal processing is then performed
on the digital signal by the digital signal processing circuit
126.
The digital signal processing circuit 126 has the capabilities of a
color separating circuit, white balance circuit, and automatic gain
control circuit. Herein, the color separating circuit separates
three color signal components of red, green, and blue signals from
a digitized signal. The white balance circuit adjusts a white
balance detected in each of the color digital signals provided by
the color separating circuit. The automatic gain control circuit
controls a gain to be given to a digital signal that has a white
balance thereof adjusted by the white balance circuit. The digital
signal processing circuit 126 carries out given digital signal
processing.
Moreover, on the stage succeeding the digital signal processing
circuit 126, there is a knee and gamma circuit 127 for treating a
knee detected by plotting each of the processed digital signals and
for correcting a gamma indicated by each thereof. The knee and
gamma circuit 127 is succeeded by a first arithmetic circuit 128.
The first arithmetic circuit 128 expands dynamic ranges for the
red, green, and blue digital signals each of which has been
processed to treat a knee and correct a gamma by means of the knee
and gamma circuit 127. The first arithmetic circuit 128 then
enhances the resultant red, green, and blue digital signals.
On the other hand, a waveform detecting circuit 123 for determining
a shutter speed for the first CCD 114 under the control of the
digital signal processing circuit 126 is connected to the digital
signal processing circuit 126. A timing generator (TG in the
drawing) 122 is connected to the waveform detecting circuit 123.
The first CCD drive circuit 121 and second CCD drive circuit 129
for driving the first CCD 114 and second CCD 115 respectively are
connected to the timing generator 122.
The waveform detecting circuit 123 is connected to a digital signal
processing circuit 132 that will be described later, and therefore
controlled by the digital signal processing circuit 132.
The waveform detecting circuit 123 detects the waveforms of digital
signals produced by the digital signal processing circuits 126 and
132, and thus determines the shutter speeds to be set for the first
CCD 114 and second CCD 115. The timing generator 122 generates
driving signals for use in driving the first CCD 114 and second CCD
115 according to an output signal of the waveform detecting circuit
123.
Moreover, the first CCD drive circuit 121 and second CCD drive
circuit 129 transmit CCD driving signals used to drive the first
CCD 114 and second CCD 115 in response to a driving signal sent
from the timing generator 122. At this time, the first CCD drive
circuit 121 and second CCD drive circuit 129 drive the first CCD
114 and second CCD 115 so that the first and second CCDs will image
an object at mutually different shutter speeds. Specifically, the
first CCD 114 is driven to image an object at a relatively low
shutter speed, while the second CCD 115 is driven to image the
object at a relatively high shutter speed. The driving control will
be described later.
The CCU 105 has a preamplifier 130, an A/D converting circuit 131,
a digital signal processing circuit 132, a knee and gamma circuit
133, and a second arithmetic circuit 134. These circuits fill the
same roles as the preamplifier 124, A/D converting circuit 125,
digital signal processing circuit 126, knee and gamma circuit 127,
and first arithmetic circuit 128. This processing system inputs an
output signal of the second CCD 115 and carries out the same
processing as that mentioned above.
Moreover, the first arithmetic circuit 128 and second arithmetic
circuit 134 are succeeded by an adder 135, a D/A converting circuit
that is not shown, and a post-processing circuit 136.
The first arithmetic circuit 128 and second arithmetic circuit 134
perform given processing on image signals that are produced at
mutually different shutter speeds by the first CCD 114 and second
CCD 115 respectively. The given processing will be detailed
later.
Output signals of the first arithmetic circuit 128 and second
arithmetic circuit 134 are added up to be thus synthesized by the
adder 135. A resultant signal is converted into an analog signal by
the D/A converting circuit, and then input to the post-processing
circuit 136. The post-processing circuit 136 converts the resultant
signal into a standard video signal. The video signal is then
output to the TV monitor 106.
Next, the operations of the endoscopic imaging apparatus 101 of
this embodiment having the foregoing components will be
described.
In this embodiment, an object image is propagated through the scope
103 by the system of relay lenses 111 that is a sole optical
system. The object image is then bisected by the pupil divider 112
in the camera head 102. Based on a driving signal generated by the
timing generator 122, the first CCD 114 and second CCD 115 project
the two equal object images provided by the pupil divider 112 at
mutually different shutter speeds. At this time, the shutter speeds
are determined by the waveform detecting circuit 123 under the
control of the digital signal processing circuit 126 and digital
signal processing circuit 132. Namely, the first CCD 114 projects
the image at a relatively low shutter speed, while the second CCD
115 projects the image at a relatively high shutter speed.
More particularly, the first CCD 114 is driven to project the
object image at a relatively low shutter speed of, for example,
1/60 sec (first exposure time). The second CCD 115 is driven to
project the object image at a relatively high shutter speed of
1/240 sec (second exposure time).
As mentioned above, the first CCD 114 and second CCD 115 project
the two equal object images provided by the pupil divider 112 at
mutually different shutter speeds. The first CCD 114 and second CCD
115 then transmit corresponding photoelectrically-converted signals
to the preamplifiers 124 and 130. CCD output signals amplified by
the preamplifiers 124 and 130 are subjected to given processing by
means of the aforesaid two systems of circuits. The first
arithmetic circuit 128 and second arithmetic circuit 135 apply
given weights to image signals produced by the first CCD 114 and
second CCD 115 respectively.
The image signals produced by the first CCD 114 and second CCD 115
are thus processed properly by the first arithmetic circuit 128 and
second arithmetic circuit 135. Thereafter, the image signals are
added up by the adding circuit 135, and then output to the
succeeding stage.
Weighting of the image signals by the first arithmetic circuit 128
and second arithmetic circuit 134, and synthesizing thereof by the
adding circuit 135 will be described with reference to FIGS. 24 and
25.
FIG. 24 is a timing chart showing the relationships among a
vertical sync signal, image signals, and a synthetic picture
signal. Herein, the vertical sync signal is output from the timing
generator 122. The image signals are actually produced by the first
CCD 114 (driven at a low shutter speed) and second CCD 115 (driven
at a high shutter speed). The synthetic picture signal is produced
by the adding circuit 135. FIG. 25 graphically shows the output
levels of image signals and the output level of a synthetic picture
signal in relation to an amount of incident light. Herein, the
image signals have been output from the first CCD 114 (driven at
the low shutter speed) and second CCD 115 (driven at the high
shutter speed), and weighted with different weights. The synthetic
picture signal is produced by the adding circuit 135.
As shown in FIG. 24, the image signal produced by the first CCD 114
during a first exposure time equivalent to the low shutter speed
(1/60 sec) shall be x. Moreover, the image signal produced by the
second CCD 115 during a second exposure time equivalent to the high
shutter speed (1/240 sec) shall be u. The synthetic picture signal
produced by the adding circuit 135 shall be M.
In this embodiment, the image signal produced by the first CCD 114
is weighted by cos.sup.2 (px) by means of the first arithmetic
circuit 128. In other words, when a luminance level is low, the
image signal produced by the first CCD 114 during the first
exposure time (1/60 sec) is weighted. Incidentally, p denotes a
correction coefficient. Assuming that a brightness level at which
the image signal produced by the second CCD 115 during the second
exposure time (1/240 sec) has a saturation value is s, the
correction coefficient p is approximately
p.apprxeq.(s.multidot..pi./2). For example, p=.pi./8.
Moreover, the second arithmetic circuit 134 applies a weight of
sin.sup.2 (px) to the image signal produced by the second CCD 115.
In other words, when a luminance level is high, the image signal
produced during the second exposure time (1/240 sec) by the second
CCD 115 is weighted.
On the other hand, the adding circuit 135 adds up the image signals
produced by the first CCD 114 and second CCD 115 and processed as
mentioned above by the first arithmetic circuit 128 and second
arithmetic circuit 134. A thus produced synthetic picture signal M
is expressed as follows:
The synthetic picture signal M exhibits the characteristic
graphically shown in FIG. 25. Thus, a dynamic range can be expanded
without any deterioration of a signal-to-noise ratio of a signal
component indicating a low luminance level.
Moreover, the correction coefficient p should merely be set
properly relative to x. The synthetic picture signal M varies as a
function that increases monotonously within a range of brightness
levels up to a brightness level at which the signal produced during
the second exposure time has the saturation value. Consequently, a
constructed image appears uniform but gives no sense of
incongruity.
In this embodiment, the correction coefficient p is approximately
.pi./8. Alternatively, the correction coefficient p may be set to
any value according to the characteristics of the first CCD 114 and
second CCD 115. In this case, the synthetic picture signal M varies
with x as a function that increases monotonously.
Moreover, the synthetic picture signal M need not vary as the above
function, that is:
Alternatively, the synthetic picture signal M may vary as a
function that has a value dominated by a signal, which is produced
at the low shutter speed, relative to a low luminance level, and
that has a value dominated by the signal, which is produced at the
high shutter speed, relative to a high luminance level.
As described above, according to this embodiment, there is provided
an endoscopic imaging apparatus that offers an expandable dynamic
range for an image signal without any deterioration of a
signal-to-noise ratio of a signal component indicating a low
luminance level. Moreover, the endoscopic imaging apparatus can
construct a smooth image giving no sense of incongruity.
Sixth Embodiment
The sixth embodiment of the present invention will be described
with reference to FIGS. 26 and 27. As shown in FIG. 26, an imaging
apparatus 150 of the sixth embodiment consists of a CCD 151, a sync
signal generating circuit (hereinafter, SSG) 157, a timing
generator (T/G in the drawing) 156, and a CCD driver (CCD DRV in
the drawing) 155. The CCd 151 is a single-plate color imaging
device for imaging an object. The sync signal generating circuit
157 generates a reference signal. The timing generator 156 inputs
the reference signal from the SSG 157 and produces a driving signal
for use in driving the CCD 151. The CCD driver 155 drives the CCD
151 in response to the driving signal sent from the timing
generator 156.
The imaging apparatus 150 further consists of a preamplifier 152, a
correlative double sampling (abbreviated to CDS) circuit 153, and
an A/D converter 154. Specifically, the preamplifier 512 amplifies
an image signal produced by the CCD 151. The CDS circuit 153
carries out correlative double sampling according to sampling
pulses sent from the timing generator 156. The A/D converter 154
digitizes an output of the CDS circuit 153. An image signal output
from the CCD 151 is amplified by the preamplifier 152. Thereafter,
the frequency of the resultant signal is lowered to fall within the
baseband by the CDS circuit 153. The signal is then digitized by
the A/D converter 154.
Moreover, the imaging apparatus 150 includes a low-shutter speed
setting unit 161 and a high-shutter speed setting unit 160. The
low-shutter speed setting unit 161 sets the shutter speed for the
CCD 151 to a low shutter speed, for example, about 1/60 sec. The
high-shutter speed setting unit 160 sets the shutter speed for the
CCD 151 to a shutter speed equivalent to a submultiple of n of the
shutter speed set by the low-shutter speed setting unit 161. Note
that the shutter speed is equivalent to an exposure time.
Thus, the data of shutter speeds is output from the low-shutter
speed setting unit 161 and high-shutter speed setting unit 160.
Either of the shutter speed is selected by a shutter speed
selection switch 159 that is changed over to a different circuit
for each field period according to a reference signal sent from the
SSG 157.
On the other hand, an output of the A/D converter 154 is sent to a
video signal processing unit that is not shown. A waveform
detecting circuit 158 is connected to the output terminal of the
A/D converter 154. The waveform detecting circuit 158 detects the
waveform of only an image signal produced by the CCD 151 at the low
shutter speed according to a field judgment signal sent from the
timing generator 156. The result of waveform detection is output to
the low-shutter speed setting unit 161.
The low-shutter speed setting unit 161 sets a shutter speed
according to the result of waveform detection performed by the
waveform detecting circuit 158, thus optimizing the level of the
image signal produced by the CCD 151.
Next, the operations of the imaging apparatus of this embodiment
having the foregoing components will be described with reference to
FIG. 27.
With a driving signal generated by the timing generator 156
according to the reference signal VD sent from the SSG 157, the CCD
driver 155 drives the CCD 151. At this time, control is given to
set a shutter speed for the CCD 151. Namely, the low shutter speed
set by the low-shutter speed setting unit 161 and the high shutter
speed set by the high-shutter speed setting unit 160 are switched
for each field period.
Moreover, the waveform detecting circuit 158 detects the waveform
of only an image signal produced at the low shutter speed set by
the low-shutter speed setting unit 161. The low-shutter speed
setting unit 161 sets a shutter speed according to a result
provided by the waveform detecting circuit 158, thus optimizing the
level of the image signal produced by the CCD 151.
On the other hand, a high shutter speed to be set by the
high-shutter speed setting unit 160 is a submultiple of n of the
shutter speed set by the low-shutter speed setting unit 161. For
example, a quarter of the shutter speed is adopted.
A photoelectrically converted signal representing an object image
projected by the CCD 151 is amplified by the preamplifier 152. The
frequency of the resultant signal is then lowered to fall within
the baseband by means of the CDS circuit 153. The signal is then
converted into a digital signal by the A/D converter 154, and
output to the video signal processing unit that is not shown.
As mentioned above, according to this embodiment, the imaging
apparatus 150 has the waveform detecting circuit 158 that detects
the waveform of only an image signal produced at the low shutter
speed set by the low-shutter speed setting unit 161. Based on the
result of waveform detection performed by the waveform detecting
circuit 158, the low-shutter speed setting unit 161 controls the
shutter speed for the CCD 151. At this time, the shutter speed for
the CCD 151 is controlled in order to optimize the level of an
image signal produced by the CCD 151. The high-shutter speed
setting unit 160 autonomously sets a higher shutter speed than the
shutter speed set by the low-shutter speed setting unit 161.
Consequently, an iris diaphragm can be realized for the CCD.
Despite the relatively simple circuitry, the imaging apparatus can
offer a wide dynamic range for an image signal.
In this embodiment, a shutter speed set by the high-shutter speed
setting unit 160 is automatically set to a quarter of a shutter
speed set by the low-shutter speed setting unit 161. Needless to
say, the submultiple of n of the shutter speed set by the
low-shutter speed setting unit 161 is not limited to the quarter
thereof.
Seventh Embodiment
Next, the seventh embodiment of the present invention will be
described with reference to FIGS. 28 and 29.
The basic configuration of an imaging apparatus 150' of the seventh
embodiment is identical to that of the sixth embodiment.
However, according to the sixth embodiment, the waveform detecting
circuit 158 detects the waveform of only an image signal produced
by a low-shutter speed. The low-shutter speed setting unit 161
controls a shutter speed according to the result of waveform
detection performed by the waveform detecting circuit 158. The
high-shutter speed setting unit 160 autonomously sets a shutter
speed according to the shutter speed set by the low-shutter speed
setting unit 161. According to this embodiment, unlike the sixth
embodiment, the waveform detecting circuit 158 detects the waveform
of only an image signal produced at a high shutter speed set by the
high-shutter speed setting unit 160. Based on the result of
waveform detection performed by the waveform detecting circuit 158,
the high-shutter speed setting unit 160 controls a shutter speed so
as to optimize the level of an image signal produced by the CCD
151. The low-shutter speed setting unit 161 sets a shutter speed
according to the shutter speed set by the high-shutter speed
setting unit 160.
Herein, a mention will therefore be made of only a difference from
the sixth embodiment. The description of duplicate portions will be
omitted.
An imaging apparatus 150' of this embodiment shown in FIG. 28
consists of a high-shutter speed setting unit 160 and a low-shutter
speed setting unit 161. Specifically, the high-shutter speed
setting unit 160 sets the shutter speed for the CCD 151 to a high
shutter speed, for example, about 1/240 sec. The low-shutter speed
setting unit 161 sets the shutter speed for the CCD 151 to a
submultiple of n of the shutter speed set by the high-shutter speed
setting unit 160. Note that the shutter speed is equivalent to an
exposure time.
Thus, the data of shutter speeds is output from the low-shutter
speed setting unit 161 and high-shutter speed setting unit 160.
Either of the shutter speeds is selected by a shutter speed
selection switch 159 that is changed over to a different circuit
for each field period according to a reference signal sent from the
SSG 157. A selected shutter speed is output to the timing generator
156.
The waveform detecting circuit 158 of this embodiment detects the
waveform of only an image signal, which is produced at a high
shutter speed by the CCD 151, according to a field judgment signal
sent from the timing generator 156. The result of waveform
detection is output to the high-shutter speed setting unit 160.
Based on the result of waveform detection performed by the waveform
detecting circuit 158, the high-shutter speed setting unit 160 sets
a shutter speed so as to optimize the level of an image signal
produced by the CCD 151.
Next, the operations of the imaging apparatus of this embodiment
having the foregoing components will be described with reference to
FIG. 29.
The timing generator 156 generates a driving signal according to a
reference signal VD sent from the SSG 157. With the driving signal,
the CCD driver 155 drives the CCD 151. The shutter speed for the
CCD 151 is controlled by switching for each field period a high
shutter speed set by the high-shutter speed setting unit 160 and a
low shutter speed set by the low-shutter speed setting unit
161.
The waveform detecting circuit 158 detects the waveform of only an
image signal produced at the high shutter speed set by the
high-shutter speed setting unit 160. Based on the result of
waveform detection performed by the waveform detecting circuit 158,
the high-shutter speed setting unit 160 sets a shutter speed so as
to optimize the level of an image signal produced by the CCD
151.
The low shutter speed set by the low-shutter speed setting unit 161
is automatically set to a multiple of n of a shutter speed set by
the high-shutter speed setting unit 160, for example, a quadruple
thereof.
A photoelectrically converted signal representing an object image
produced by the CCD 151 is amplified by a preamplifier 152.
Thereafter, the frequency of the resultant signal is lowered to
fall within the baseband by means of a CDS circuit 153. The signal
is then converted into a digital signal by an A/D converter 154,
and then output to a video signal processing unit that is not
shown.
As mentioned above, even in the imaging apparatus 150' of this
embodiment, like that of the sixth embodiment, an iris diaphragm
can be realized for the CCD. Despite the relatively simple
circuitry, the imaging apparatus can offer a wide dynamic range for
an image signal.
Even in this embodiment, a shutter speed set by the low-shutter
speed setting unit 161 is a quadruple of a shutter speed set by the
high-shutter speed setting unit 160. Naturally, the multiple of the
shutter speed set by the high-shutter speed setting unit is not
limited to the quadruple thereof.
Eighth Embodiment
Next, the eighth embodiment of the present invention will be
described with reference to FIGS. 30 and 31.
The same reference numerals will be assigned to components
identical to those of the sixth and seventh embodiments. The
description of the components will be omitted.
In the imaging apparatuses 150 and 150' of the sixth and seventh
embodiment, the waveform of either an image signal produced at a
low shutter speed or an image signal produced at a high shutter
speed is detected. Either the low shutter speed or high shutter
speed is set based on the result of waveform detection. The other
shutter speed is set to a certain ratio of the set shutter
speed.
Unlike the imaging apparatuses of the embodiments, an imaging
apparatus 150" of this embodiment detects the waveform of an image
signal produced at a low shutter speed and that of an image signal
produced at a high shutter speed. The high-shutter speed setting
unit 160 and low-shutter speed setting unit 161 each set a shutter
speed.
As shown in FIG. 30, the imaging apparatus 150" of this embodiment
includes a high-shutter speed setting unit 160 and a low-shutter
speed setting unit 161. The high-shutter speed setting unit 160
sets the shutter speed for the CCD 151 to a high shutter speed, for
example, about 1/240 sec. The low-shutter speed setting unit 161
sets the shutter speed for the CCD 151 to a low shutter speed, for
example, about 1/60 sec.
Thus, the data of shutter speeds is output from the low-shutter
speed setting unit 161 and high-shutter speed setting unit 160.
Either of the shutter speeds is, like those in the sixth and
seventh embodiments, selected by a shutter speed selection switch
162 that is changed over for each field period according to a
reference signal sent from the SSG 157. The data of the selected
shutter speed is then output to the timing generator 156.
On the other hand, the waveform detecting circuit 158 of this
embodiment detects the waveforms of image signals produced by the
CCD 151 according to a field judgment signal sent from the timing
generator 156. Herein, one of the image signals has been produced
at a high shutter speed, and the other image signal has been
produced at a low shutter speed. The results of waveform detection
are output to either the high-shutter speed setting unit 160 or
low-shutter speed setting unit 161. Either the high-shutter speed
setting unit 160 or low-shutter speed setting unit 161 is selected
by a shutter setting unit selection switch 163 that is changed over
for each field period according to the reference signal sent from
the SSG 157.
The high-shutter speed setting unit 160 or low-shutter speed
setting unit 161 is selected by the shutter setting unit selection
switch 163. At this time, based on the results of waveform
detection performed by the waveform detecting circuit 158, a
shutter speed is determined in order to optimize the level of an
image signal produced by the CCD 151.
Next, the operations of the imaging apparatus 150" of this
embodiment having the foregoing components will be described with
reference to FIG. 32.
The timing generator 156 generates a driving signal according to a
reference signal VD sent from the SSG 157. With the driving signal,
the CCD driver 155 drives the CCD 151. At this time, the shutter
speed for the CCD 151 is controlled so that a high shutter speed
set by the high-shutter speed setting unit 160 and a low shutter
speed set by the low-shutter speed setting unit 161 will be
switched for each field period.
Moreover, the waveform detecting circuit 158 detects the waveforms
of both an image signal produced at the high shutter speed and an
image signal produced at the low shutter speed. The results of
waveform detection are output to either the high-shutter speed
setting unit 160 or low-shutter speed setting unit 161 selected by
the shutter setting unit selection switch 163.
A shutter setting unit selected by the shutter setting unit
selection switch 163 determines a shutter speed according to
results provided by the waveform detecting circuit 158. In other
words, a shutter speed is determined in order to optimize the level
of an image signal produced by the CCD 151.
A photoelectrically converted signal representing an object image
produced by the CCD 151 is amplified by the preamplifier 152.
Thereafter, the frequency of the signal is lowered to fall within
the baseband by means of the CDS circuit 153. The resultant signal
is converted into a digital signal by the A/D converter 154. The
digital signal is then output to the video signal processing unit
that is not shown.
As mentioned above, according to this embodiment, the imaging
apparatus 150" can offer an optimal dynamic range for an image
signal according to the brightness levels of an object. Even an
object that may be visualized with a quite bright portion and quite
dark portion thereof coexistent on the same screen can be imaged
without occurrence of any drawback such as streaky whitening or
blackening.
In the sixth to eighth embodiments, imaging at a low shutter speed
and imaging at a high shutter speed are switched for each field
period that is defined by the timing generator 156. The present
invention is not limited to this mode. Alternatively, as shown in
FIG. 32, imaging at the low shutter speed may be repeated over a
plurality of field periods.
When imaging at the low shutter speed is carried out in a long
exposure mode, a proper dynamic range can be offered even for a
very dark object. In this example, the waveform detecting circuit
158 can be excluded.
As mentioned above, according to the sixth to eighth embodiments,
there is provided an endoscopic imaging apparatus capable of
constructing an appropriate image even when the brightness level of
an object varies widely.
Ninth Embodiment
Next, the ninth embodiment of the present invention will be
described with reference to FIGS. 33 to 40. An endoscopic imaging
apparatus 201 of the ninth embodiment of the present invention will
be described in conjunction with a schematic configuration shown in
FIG. 33.
In the endoscopic imaging apparatus 201, light reflected from an
object of observation 202 falls upon an imaging unit 204 through an
optical path 203. An exposure value control means 205 in the
imaging unit 202 controls an amount of incident light reflected
from the object of observation 202. For constructing one frame
image, the amount of incident light is controlled so that an
exposure value will be different between two field periods. Thus,
an exposure value for the imaging surface of an imaging device 206
is controlled.
The exposure value control means 205 sets the exposure value for
the imaging surface so that an image prone to streaky whitening
(halation) will be formed during a first field, and an image prone
to slight blackening (blacking out) will be formed during a second
field period.
An image processing unit 207 includes a signal generator 298 for
generating a timing signal used to switch the actions of the
exposure value control means 205 according to given timing. Herein,
a timing signal used to change exposure values for each field
rendered by a video signal is sent to the exposure value control
means 205.
In the image processing unit 207, an amplifier 209 amplifies an
image signal that has been photoelectrically converted by the
imaging device 206 and input to the image processing unit.
Thereafter, an image processing circuit 210 synthesizes signals,
which render a first field and second field, according to a given
algorithm, thus producing a video signal.
In synthesis for producing a video signal, a timing signal sent
from the signal generator 208 is used to lock the timing of an
image signal produced by the imaging device 206 onto the timing of
a reference signal. A video signal produced is output to an image
display 212 such as a CRT monitor via a video output circuit 211.
An image of the object of observation 202 is then displayed.
Owing to the foregoing components, a relatively dark portion of a
view image is displayed based on an image signal that renders a
first field and is prone to streaky whitening. Moreover, a
relatively bright portion thereof is displayed based on an image
signal that renders a second field and is prone to blackening.
Consequently, the view image is seen clearly proving a wide dynamic
range. In other words, it will not take place that blackening stems
from an insufficient amount of light and streaky whitening stems
from an excess amount of light.
FIG. 34 shows a configuration of an endoscopic imaging unit 204A as
a practical example of the imaging unit 204. The endoscopic imaging
unit 204A consists of an optical endoscope 215, and a camera head
216 or TV camera mounted on the optical endoscope 215. The optical
endoscope 215 has an elongated insertion unit 217 that is inserted
into a body cavity or the like.
A light guide 218 for propagating illumination light is running
through the insertion unit 217. The proximal end of the light guide
218 is coupled to a light source unit 220 through a light guide
cable 219. Thus, illumination light emanating from a lamp 222 that
glows with power supplied from a lamp power supply circuit 221 is
converged by a lens and then supplied. The illumination light is
propagated and emitted through the distal end of the light guide
218. Consequently, an object 223 that is the object of observation
202 is illuminated.
Light reflected from the object 223 illuminated by the illumination
light is passed through an objective optical system 224 located at
the distal end of the insertion unit 217. An optical image of the
object is formed on the distal surface of an image guide 225, and
propagated to the back surface of the image guide 225 by means of
the image guide 225. The optical image propagated to the back
surface is projected on a CCD 228 placed as the imaging device 206
on the image plane of an image formation lens 227.
A mosaic filter 229 for separating color components is attached to
the imaging surface of the CCD 228. When a CCD driving signal
generated by the signal generator 208 is applied to the CCD 228, a
photoelectrically converted picture signal is output.
According to this embodiment, a disk-like filter member 231 is
placed as the exposure value control means 205 on an optical path
linking the image formation lens 227 and CCD 228. The filter member
231 is driven to rotate by means of a motor 232 that rotates with a
driving signal sent from a motor control circuit 233. A field
judgment signal whose level differs between a first field and
second field is input to the motor control circuit 233. The motor
control circuit 233 controls rotation of the motor so that two
filters 234a and 234b of the filter member 231, which are shown in
FIG. 35A, will be placed on the optical path alternately for each
field. Thus, an amount of imaging light to be projected on the CCD
228 is controlled field by field.
In other words, as shown in FIGS. 35A and 35B, the filter member
231 is composed of two kinds of filters Fa and Fb shaped
semi-circularly and mutually different in transmittance. An axial
member is extended from the center of the filter member 231 in a
normal direction. The other end of the axial member is fitted in
the motor 232. The filter member 231 is therefore rotated together
with rotation of the motor 232.
A description will proceed on the assumption that one of the two
kinds of filters Fa and Fb of the filter member 231 exhibiting
different characteristics, that is, the filter Fa offers a higher
transmittance than the filter Fb.
In this case, as mentioned above, an image signal rendering a first
field is produced to be prone to streaky whitening. An image signal
rendering a second field is produced to be prone to blackening. The
motor 232 is driven so that the filter Fa will face the imaging
surface of the CCD 228 during a first field period, and the filter
Fb will face it during a second field period.
In other words, the motor 232 makes one turn during one frame
period. The filter Fa faces the imaging surface during a first half
of the frame period, that is, a first field period. The filter Fb
faces the imaging surface during a second field period.
The transmission characteristics of the two kinds of filters Fa and
Fb vary depending on the state of an object to be imaged. Assume
that an amount of light reflected from an object of observation
remains constant. In this case, the amount of light reflected from
the object of observation is all projected on a portion of the
imaging surface of the CCD 228 used to render a first field. For
example, a several submultiple of the light reflected from the
object of observation, or a several tens submultiple thereof is
projected on the other portion thereof used to render a second
field. For the same object 23, two images rendering the first field
and second field are projected with different amounts of light.
In this embodiment, normally adopted conditions for imaging (for
example, one frame imaging period is 1/30 sec, and each field
period is 1/60 sec) are satisfied. The relative transmission
characteristics of the filters Fa and Fb are differentiated from
each other. Nevertheless, images can be projected with an exposure
value made greatly different between them. For projecting images
with an exposure value made greatly different between them, the
transmission characteristics of the filters Fa and Fb should merely
be differentiated from each other.
Imaging is thus controlled. Consequently, when the filter Fa exists
on the optical path, an amount of light passing through the filter
member 31 (that is, an amount of light incident on the CCD 228)
varies according to a characteristic curve A in FIG. 36. When the
filter Fb exists on the optical path, an amount of light passing
through the filter member 231 varies according to a characteristic
curve B in FIG. 36.
Since imaging is thus controlled, a field judgment signal (See FIG.
37A) output from the signal generator 208 incorporated in the image
processing unit 7 is input to the motor control circuit 233. As
shown in FIG. 37B, control is given so that the filter Fa will be
located on the optical path during a first field period and the
filter Fb will be located thereon during a second field period. As
shown in FIG. 37C, when the filter Fa is located on the optical
path, an amount of incident light is large. When the filter Fb is
located on the optical path, an amount of incident light is
smaller.
Consequently, different images are projected with different amounts
of light during the first and second field periods.
A signal processing system for displaying a constructed image on
the image display 212 such as a typical TV monitor will be
described below.
Image signals produced as mentioned above to render fields are
processed by the image processing unit 207. FIG. 38 shows a
configuration of a video processor 237A as a practical example of
the image processing unit 207.
A CCD driver 241 operates synchronously with a timing signal
generated by the timing generator 240. The CCD driver 241 applies a
CCD driving signal to the CCD 228 at the start of each field
period. An optical image projected on the imaging surface of the
CCD 228 during each field period is photoelectrically converted.
Charges accumulated during one field period to serve as a signal
are read from the CCD 228. An output signal is amplified by an
amplifier 242, and then passed through a pre-processor A/D
converter 243. Pre-processing such as correlative double sampling
is carried out in order to extract signal components. The resultant
signal is then digitized.
Thereafter, the signal is input to a dynamic range expander 244
that carries out wide dynamic range processing. After the wide
dynamic range processing is completed, a color separation and white
balance and AGC unit 245 carries out color separation, white
balance adjustment, and AGC. Thereafter, a resultant signal is
output to an external monitor or the like via a D/A converter
post-processor 246.
The color separation and white balance and AGC unit 245 has a frame
memory. A field signal is read from the frame memory according to,
for example, the interlacing. On a stage succeeding the unit 245,
the signal is converted into an analog signal and output as a
composite video signal conformable to the NTSC. Alternatively, the
signal may not be output as a composite video signal conformable to
the NTSC but may be output as red, green, and blue signals.
FIG. 39 shows a practical example of the dynamic range expander 244
shown in FIG. 38. FIGS. 40A to 40G are timing charts for explaining
the actions of the dynamic range expander 244 shown in FIG. 39. VD
in FIG. 40 denotes a vertical sync signal.
A digitized video signal input to the dynamic range expander 244
shown in FIG. 39 is input to a frame memory 247. (In FIGS. 40C and
40D, An and Bn denote signals produced during first and second
field periods of the n-th frame period.) The video signal is also
input to first and second selectors 248a and 248b.
The video signal input to the frame memory 247 is input to the
first and second selectors 248a and 248b on a first-in first-out
(FIFO) basis. Namely, input of the signal to the second selector
lags behind by one field period (See FIGS. 40C and 40D). In other
words, output of the signal from the second selector lags behind by
one field period. The signal is therefore output synchronously with
a signal rendering a subsequent field.
A field judgment signal shown in FIG. 40B is input directly to the
first selector 248a but input to the second selector 248b via a
reversing circuit 249. With the field judgment signal as a
reference, either of signals rendering first and second fields and
existing in the selectors is fetched.
A signal input to the first selector 248a is output to a first
multiplier 250a. First and second look-up tables (LUTs) 251a and
251b are referenced based on the signal. The signal is then
weighted with appropriate functions.
The functions are, for example, as shown in FIGS. 40E and 40F,
cos.sup.2 (pB) residing in the first LUT 251a and sin.sup.2 (pB)
residing in the second LUT 251b. The variable pB in the function
cos or sin varies with a brightness level B of an object ranging
from 0 to .pi./2, though it depends on the parameter p for
converting one scale to another. Herein, the brightness level B is
equivalent to a luminance level of a pixel to be produced with a
limited amount of incident light. An image signal produced under
the condition that an amount of incident light is limited is
employed. This is because when an image signal produced under any
other condition is employed, the image signal may have a saturation
value. Thus, the image signal produced with a limited amount of
incident light is employed in order to avoid use of such an image
signal having a saturation value.
cos(pB) is a function that decreases monotonously relative to a
brightness level of an object. sin(pB) is a function that increases
monotonously. Squares of the functions exhibit similar
characteristics. In this case, the sum of the squared functions is
1.
Signals weighted by referencing the first and second LUTs 251a and
251b are output to the first and second multipliers 250a and 250b.
The signals are then multiplied by outputs of the first and second
selectors 248a and 248b. Thereafter, outputs of the first and
second multipliers 250a and 250b are added up by an adder 252. A
resultant signal is output from the dynamic range expander 244 as
shown in FIG. 40G.
As mentioned above, two images constituting one frame and projected
with different amounts of light during two field periods are
synthesized with each other in order to construct one image
rendering the one frame. A signal proving a wide dynamic range is
thus produced, and output to an external monitor or the like via a
processing system on a succeeding stage.
As mentioned above, two images are projected on the imaging
surfaces of the CCD 228 with different amounts of light, which are
defined by the filters Fa and Fb, during two field periods that are
mutually identical imaging periods. Signals representing the images
produced with the different amounts of light are weighted and
synthesized into one picture signal proving a wide dynamic range by
means of a signal processing system including the video processor
237A. The picture signal is then recomposed into a standard video
signal. Eventually, an image is displayed on the image display
means.
According to this embodiment, an imaging means having a filtering
means is used in combination with an image processing unit.
Consequently, an endoscopic imaging apparatus for constructing an
image of good quality, which proves a wide dynamic range, despite
the simple configuration can be realized.
In other words, according to a prior art, for constructing a
synthetic picture signal proving a wide dynamic range, two imaging
periods must be mutually greatly differentiated. According to this
embodiment, the two imaging periods have the same length. Despite
the simple signal processing system, the synthetic picture signal
can be produced to be unsusceptible to noises or a motion of an
object. In other words, a view image of good quality can be
displayed according to the synthetic picture signal proving a wide
dynamic range.
According to this embodiment, a synthetic picture signal proves a
wide dynamic range. Besides, the synthetic picture signal exhibits
a characteristic that a luminance level or tone detected therein
varies smoothly while reflecting a change in brightness of an
object. An image reflecting a delicate color change of the object
can therefore be seen. Consequently, an image helpful in locating
an initial-stage lesion or diagnosing the lesion properly can be
presented.
Tenth Embodiment
In the ninth embodiment, a simultaneous type illuminating means and
imaging means are employed in color imaging under illumination of
white light. Imaging using a field-sequential type illuminating
means and imaging means will be described below.
An endoscopic imaging unit 204B shown in FIG. 41 is different from
the one shown in FIG. 34 in a point described below. Namely, a
light source unit 220' shown in FIG. 41 is configured by placing an
RGB rotary filter 234b to be rotated by a motor 234a on an optical
path of illumination light in the light source unit 220 shown in
FIG. 34.
As shown in FIG. 42, the RGB rotary filter 234b has three sector
windows bored in a disk. The windows are covered with red, green,
and blue filters 200R, 200G, and 200B that transmit rays with the
wavelengths of red, green, and blue. The RGB rotary filter 234b is
rotated by the motor 234a. Illumination light rays of red, green,
and blue are supplied successively to the light guide 218, and then
propagated by the light guide. Consequently, the object 223 is
illuminated with the field-sequential light rays of red, green, and
blue.
Moreover, a camera head 216' shown in FIG. 41 employs a monochrome
CCD 228. The monochrome CCD 228 does not have the mosaic filter 229
for separating color signal components which is attached to the
imaging surface of the CCD 228 in the camera head 216 shown in FIG.
34. A filter member 235 shown in FIG. 43 is substituted for the
filter member 231.
Specifically, the wheel-shaped filter member 235 is attached to the
front surface of the CCD 228. The filter member 235 is composed of
a total of six filters Ra, Ga, Ba, Rb, Gb, and Bb, or three pairs
of two kinds of filters offering different transmittances. The
three pairs are provided for three colors of red, green, and
blue.
FIG. 44 shows a configuration of a video processor 237 adopting the
foregoing field-sequential method. Processing to be carried out on
stages preceding a dynamic range expander 244' is nearly identical
to the processing to be carried out on the stages shown in FIG. 38.
An output signal of the dynamic range expander 244' is output as
red, green, and blue color signals via D/A converting circuits
255R, 255G, and 255B. Consequently, signals Y/C and VBS are output
via an encoder 256.
In this case, as shown in FIG. 43, the red filter Ra, green filter
Ga, blue filter Ba, red filter Rb, green filter Gb, and blue filter
Bb are arranged in that order. Herein, the red filter Ra, green
filter Ga, and blue filter Ba offer high transmittances. The red
filter Rb, green filter Gb, and blue filter Bb offer low
transmittances.
In other words, as shown in FIG. 43, the Ra transmittance is higher
than the Rb transmittance, the Ga transmittance is higher than the
Gb transmittance, and the Ba transmittance is higher than the Bb
transmittance.
FIGS. 45A to 45F are explanatory diagrams indicating the actions of
the imaging means. In this case, field-sequential rays of red,
green, and blue are fetched sequentially. Red, green, and blue
judgment signals shown in FIGS. 45A, 45B, and 45C are therefore
employed in imaging. A field-sequential field judgment signal shown
in FIG. 45D is also employed.
As shown in FIG. 45E, the filters Ra, Ga, and Ba are placed
sequentially on the optical path during a first field period during
which the field-sequential field judgment signal is high. The
filters Rb, Gb, and Bb are placed sequentially on the optical path
during a second field during which the field-sequential field
judgment signal is low. An exposure value is controlled so that an
amount of incident light will, as shown in FIG. 45F, be different
between the first and second field periods.
For example, for fetching a red signal, the red judgment signal is
driven high and the field-sequential field judgment signal
(hereinafter, field signal) is driven high. At this time, the
filter Ra is placed in front of the CCD 228. When the red judgment
signal is driven high and the field signal is driven low, the
filter Rb is placed in front of the CCD 228.
During the first field period, a larger amount of light can be
routed to the CCD 228 than during the second field period.
Image signals produced during the first and second field periods
are input to the video processor 237B serving as an image
processing unit. Given image processing for expanding a dynamic
range is then performed on the signals. This results in a red
signal proving a wide dynamic range. Moreover, the ratio of the
transmittance offered by the filter Ra to that offered by the
filter Rb depends on a purpose of use. Any ratio is conceivable in
the range from, for example, a ratio of 3 to 1 to a ratio of
several tens to 1.
The same applies to green and blue signals. Green and blue signals
proving wide dynamic ranges can be constructed. When the red,
green, and blue signals are encoded according to a known method, a
video signal proving a wide dynamic range can be produced.
As apparent from FIGS. 45A to 45F, the filter member 235 makes one
turn during one frame period.
Even in this embodiment, the filter member 235 is used for imaging.
In principle, image signals can be produced with an exposure value
differentiated between them without any change between imaging
periods.
In this embodiment, the configuration and actions of the dynamic
range expander 244' shown in FIG. 44 are different from those of
the one shown in FIG. 38. This is because an input signal of the
dynamic range expander 244' is divided into red, green, and blue
signal components. FIG. 46 shows the configuration of the dynamic
range expander 244'.
A digital video signal input to the dynamic range expander 244'
contains signal components of red, green, and blue signals
rendering a first field and those rendering a second field. The
red, green, and blue signals are input during a period coincident
with one cycle of the field-sequential field judgment signal.
Assume that the cycle of the field-sequential field judgment signal
agrees with that of the field judgment signal shown in FIG. 40B. In
this case, for separating the red, green, and blue signal
components from the input signal of the dynamic range expander
244', only a one-third of a field period is utilized for separating
each signal component.
A digital video signal input to the dynamic range expander 244' is
first input to a signal selector interpolator 261 in the dynamic
range expander 244'. Each color signal component of the video
signal is decoded and interpolated in order to stretch the cycle of
each color signal component to a triple. Resultant color signals
are output from the signal selector interpolator 261.
Thereafter, signal processing indicated in FIGS. 39 and 40A to 40G
is carried out in order to produce red, green, and blue digital
signals. FIG. 46 shows a practical configuration of the dynamic
range expander 244' for carrying out the processing. FIGS. 47A to
47I are explanatory diagrams schematically showing inputs and
outputs of the signal selector interpolator 261.
Referring to FIG. 46, for example, a red signal output from the
signal selector interpolator 261 is input to a red frame memory
247R. The red signal is also input to first and second selectors
for red (red first SEL and red second SEL in FIG. 46) 248Ra and
248Rb. Moreover, an output of the red frame memory 247R is input to
the first and second selectors for red 248Ra and 248Rb.
A field judgment signal is input to the first and second selectors
for red 248Ra and 248Rb directly and via a reversing circuit 249R.
Output signals of the first and second selectors for red 248Ra and
248Rb are input to multipliers 250Ra and 250Rb.
Moreover, an output signal of the first selector for red 248Ra is
input to first and second LUTs 251Ra and 251Rb. Output signals of
the first and second LUTs 251Ra and 251Rb are multiplied by output
signals of the first and second selectors for red 248Ra and 248Rb
by means of the multipliers 250Ra and 250Rb. Resultant signals are
added up by an adder 252R. Consequently, a digital red signal is
output to a succeeding stage.
The same circuit elements as those mentioned above are provided for
the other color signals of green and blue. The alphabet R appended
to the reference numerals denoting the circuit elements should
merely be replaced with G or B. The description of the circuit
elements bearing the letters G and B will be omitted.
The circuit elements succeeding the signal selector interpolator
261 in the dynamic range expander 244' are realized by triplicating
the dynamic range expander 244 in FIG. 39 in relation to the color
signal components.
Moreover, the signal selector interpolator 261 separates color
signal components that will be input sequentially during three
sub-periods within each period within which the field-sequential
field judgment signal is high or low. The signal selector
interpolator 261 then stretches the cycles of the color signal
components into triples, and then outputs resultant signals to the
red, green, and blue frame memories through red, green, and blue
output terminals thereof.
The dynamic range for each color signal is then expanded as
indicated in FIGS. 40A to 40G in the same manner as that performed
by the configuration shown in FIG. 39. (In this case, for producing
a red color signal, the frame memory input shown in FIG. 40C is
regarded as an input of the red frame memory.)
In this embodiment, as shown in FIGS. 45A to 45C, independent
judgment signals are used for red, green, and blue signals.
However, the employment of the three color signals alone makes it
possible to discriminate among the red, green, and blue signals or
between first and second fields. FIGS. 48A to 48E are timing charts
indicating the discrimination.
In this case, two kinds of color judgment signals and a
field-sequential field judgment signal are used in combination to
judge an amount of light incident on an imaging device and
discriminate among red, green, and blue signals.
Specifically, referring to FIGS. 48A to 48E, when first and second
color judgment signals C1 and C2 are high and low respectively, a
red signal is identified. When the first and second color judgment
signals C1 and C2 are low and high respectively, a green signal is
identified. When the first and second color judgment signals C1 and
C2 are both high, a blue signal is identified. The first and second
color judgment signals are used in combination with the
field-sequential field judgment signal, thus providing the same
effect as the practical example described in conjunction with FIGS.
45A to 45F.
Moreover, the two color judgment signals may be substituted for the
red, green, and blue judgment signals shown in FIG. 46.
Nevertheless, the signal selector interpolator 261 can separate
color signal components and stretch the cycles of the color signal
components. The dynamic ranges for the color signals can be
expanded on a succeeding stage.
In this case, a wheel-shaped filter member employed will be
identical to the filter member 235 shown in FIG. 43. Moreover, a
second variant of this embodiment is conceivable. In the second
variant, the filters are not arranged in the order of the filters
Ra, Ga, Ba, Rb, Gb, and Bb but may be arranged in the order of the
filters Ra, Rb, Ga, Gb, Ba, and Bb. A wheel-shaped filter member
having the filters thus arranged will be described below.
FIG. 49 shows a wheel-shaped filter member 235'.
FIGS. 50A to 50F are timing charts indicating the actions of an
imaging means having the filter member. Since the filter member
235' has filters arranged as shown in FIG. 49, unlike the timing
charts of FIGS. 45A to 45F, two color signals of red, green, or
blue rendering first and second fields are produced consecutively.
Two color signals are produced in the order of red, green, and
blue. Thereafter, a color signal of red rendering the first field
is produced. This sequence is repeated.
Except for the arrangement of filters and the timing of signals,
imaging control is fundamentally identical to that indicated in
FIGS. 45A to 45F. The details of imaging control will therefore be
omitted. The basic idea is to produce an image rendering a first
field with a large amount of light incident on the imaging surface,
and an image rendering a second field with a small amount of
incident light. An image proving a wide dynamic range is thus
constructed.
For a better understanding of the second variant, FIGS. 50G to 50I
that are timing charts present an example of imaging control that
exerts the same effect as imaging control presented by FIGS. 45A to
45D. In this example, the three judgment signals shown in FIGS. 48A
to 48C are utilized, and the filter member 235' shown in FIG. 49 is
employed.
A block diagram showing a basic configuration for processing a
signal using the filter member 235' is nearly identical to that of
FIG. 44 or 46. Only a difference in signal processing lies in that
images rendering a first field and second field are projected
successively on the imaging surface in a single color. FIGS. 51A to
51I are timing charts indicating the timing for the image
signals.
In FIGS. 51A to 51I, Ron (where o stands for odd, and n is 0, 1, 2,
3, etc.) denotes a component of each of red, green, and blue
signals rendering a first field (odd field). Ren (where e stands
for even, and n is 0, 1, 2, 3, etc.) denotes a component thereof
rendering a second field (even field).
In this case, a dynamic range expander has a configuration
including a signal selector interpolator 261' shown in FIG. 52 in
place of the signal selector interpolator 261 shown in FIG. 46.
A video signal is input to a decoder 263 via a buffer 262. An
output signal of the decoder 263 is input to red, green, and blue
signal stretching circuits 264R, 264G, and 264B. Based on an
externally input control signal, a decoder stretch control circuit
265 applies a control signal for controlling the decoder 263 and
red, green, and blue stretching circuits.
In response to the control signal, the input video signal is
decoded by the decoder 263. After decoded, each of red, green, and
blue color signals is stretched by interpolating signal components
occurring during a period defined by a field signal. Resultant red,
green, and blue signals whose cycles have been stretched are stored
temporarily in frame memories 266R, 266G, and 266B, and output to a
succeeding stage successively on a FIFO basis. The signal selector
interpolator 261' is used to expand dynamic ranges as shown in FIG.
46.
Specifically, red, green, and blue signal components are, as
mentioned above, extracted from a digital video signal input to the
signal selector interpolator 261'. Thereafter, the red, green, and
blue signals have the cycles thereof stretched to triples as
indicated in FIGS. 51A to 51I. Resultant signals are then stored in
the red, green, and blue frame memories 247R, 247G, and 247B.
The red, green, and blue signals output from the frame memories are
processed to expand dynamic ranges, and then output to an external
monitor or the like via a D/A converter.
According to this embodiment and its variants, an imaging device
whose operating speed is low is used to expand a dynamic range in
substantially the same manner as when a simultaneous type imaging
device is used. An imaging device whose operating speed is high
need not be procured.
Eleventh Embodiment
Next, the eleventh embodiment of the present invention will be
described. This embodiment uses a liquid crystal device as an
exposure value control device. The liquid crystal device of this
embodiment is not a device having the capability of a shutter for
switching transmission and non-transmission by turning on or off a
control signal. An employed device is characteristic of restricting
an amount of light incident on an imaging device by scattering the
incident light when the control signal is on.
FIG. 53 shows a configuration of a major portion of an imaging
unit. A camera head 216B has a liquid crystal device (LCD) 271
interposed between the lens 227 and CCD 228 shown in FIG. 34. The
LCD 271 is controlled by a liquid crystal device drive unit (LCD
drive) 272.
A field judgment signal is input to the LCD drive unit 272. For
example, as shown in FIG. 54A, the field judgment signal is high
during a first field period (odd field period). At this time, an
LCD driving signal is low as shown in FIG. 54B. During a second
field period (even field period) during which the field judgment
signal is low, the LCD driving signal is driven high.
When the LCD driving signal is driven high, the transmittance of
the LCD is lowered as shown in FIG. 54C. Incident light is routed
to the CCD 228. An image is formed with an exposure value
decreased. When the LCD driving signal is driven low, the
transmittance is raised. Incident light is thus routed to the CCD
228. An image is formed with the exposure value increased.
The LCD drive unit 272 is incorporated in the camera head 216B in
FIG. 53. For compactly designing the camera head 216B that is an
imaging unit, the LCD drive unit may be incorporated in the image
processing unit 207. In either case, the LCD drive unit 272 has the
ability to control the actions of the LCD 271.
Based on an input field judgment signal, the LCD drive unit 272
generates an LCD driving signal of a proper voltage for driving a
liquid crystal in the LCD 271. The signal is applied to the liquid
crystal in order to control the orientation of liquid crystalline
molecules, whereby an amount of light transmitted by the LCD 271 is
controlled.
More particularly, for forming an image prone to streaky whitening,
a low voltage is applied to the LCD 271 so that the liquid
crystalline molecules will be aligned in a direction in which
incident light propagates. For forming an image prone to
blackening, a high voltage is applied to the LCD 271 so that the
liquid crystalline molecules will be orthogonal to the direction in
which incident light propagates.
In this configuration, a signal processing system identical to that
of the ninth embodiment can be employed.
As mentioned above, both images prone to streaky whitening and
blackening can be formed. Consequently, an image of good quality
proving a wide dynamic range can be constructed by setting
appropriate algorithms in the image processing unit 7.
According to this embodiment, the mechanically movable feature
employed in the ninth embodiment is unnecessary. Nevertheless,
substantially the same operations and advantages as those of the
ninth embodiment can be provided.
Moreover, a liquid crystal device (LCD) may function as an almost
perfect shutter according to the on or off state of an input
control signal.
A variant using an LCD functioning as a shutter will be described.
In this variant, the layout of the LCD 271 and others in an imaging
unit is identical to that shown in FIG. 53.
When signals are driven as indicated in the timing charts of FIGS.
54A to 54C, no light falls on the CCD 228 during an even field
period. A completely blackened image alone is formed.
During only a proper sub-period within the even field period, the
LCD 271 is broken. During the other time, the LCD 271 is made. In
this way, for example, unlike during an odd field period, an amount
of light incident on the imaging surface of the CCD 228 is limited
during the even field period. Consequently, the same advantages as
those provided by the imaging unit, which is shown in FIG. 53 and
whose actions are indicated in FIGS. 54A to 54C, can be
provided.
FIGS. 55A to 55C are timing charts in accordance with the variant.
In this variant, an amount of light falling on the CCD 228 during
an even field period is set to a half of an amount of light falling
thereon during an odd field period. A non-transmission period
(during which the shutter is closed) is a half ta of the even field
period tb. Alternatively, the non-transmission period may be set
arbitrarily according to the state of an object to be imaged or a
purpose of use. For example, the non-transmission period may be set
to a several submultiple of the even field period or a several
hundreds submultiple thereof.
Even in this variant, the CCD driving signal for driving the CCD
228 is driven once during each field period, that is, twice during
one frame period as it is in the first embodiment.
This variant provides almost the same advantages as the tenth
embodiment. For example, the sub-period within the even field
period during which the LCD driving signal is driven high may be
variable. In this case, the CCD driving signal may not be varied.
Nevertheless, images can be formed by arbitrarily changing the
ratio of an exposure value for one image to that for another
image.
For example, a brightness level of an object is detected. If the
brightness level is high, the sub-period within the even field
period during which the LCD driving signal is driven high is
shortened in order to form an image with an exposure value
decreased.
The image formed with the decreased exposure value and another
image are synthesized with each other. A resultant image is
processed to expand a dynamic range. Thus, even when an object
exhibits a high brightness level, a view image whose high-luminance
level portion will not have a saturation value can be
constructed.
Twelfth Embodiment
Next, an endoscopic imaging apparatus of the twelfth embodiment of
the present invention will be described.
As presented in the ninth to eleventh embodiments, for constructing
an image that proves a wide dynamic range, an amount of light
incident on the imaging device 206 is controlled. Thus, an image
prone to streaky whitening and an image prone to blackening are
formed to render two fields.
In general, when extraneous natural light is insufficient, if an
imaging apparatus is used in combination with, for example, an
endoscope, a light source unit must be prepared additionally in
order to ensure a necessary amount of light. In this case, an
amount of light reflected from an object of observation is limited
by an amount of light emanating from the light source unit. If the
amount of light emanating from the light source unit can be
controlled, an exposure value (an amount of incident light) may be
controlled according to a technique different from the one adopted
in the ninth embodiment to thirteenth embodiment. By properly
controlling timing, an image prone to streaky whitening and an
image prone to blackening can be formed. This embodiment adopts
this idea.
The ninth embodiment to eleventh embodiment can be adapted to an
imaging apparatus not including a light source unit. In other
words, the ninth to eleventh embodiments can be adapted to an
imaging apparatus that does not always requires a light source
unit, such as, a video camera.
FIG. 56 schematically shows a configuration of an endoscopic
imaging apparatus 274 of the twelfth embodiment. The endoscopic
imaging apparatus 274 has an imaging unit 204' not including the
exposure value control means 205 that is included in the imaging
unit 204 shown in FIG. 33. Instead, an amount-of-emitted light
control means 277 is included in a light source unit 276 having a
light emitting means 275 incorporated therein. An amount of emitted
light propagated over the optical path 203 by way of a light guide
278 in order to illuminate the object of observation 202 is then
controlled.
Moreover, an image processing unit 207' has a light adjusting
circuit 279 interposed between the image processing circuit 210 and
signal generator 208 that are included in the image processing unit
207 shown in FIG. 33. A signal sent from the image processing
circuit 210, which processes an image signal output from the
imaging device 206, is input to the light adjusting circuit 279. A
control signal is then produced to control the light emitting means
275. Moreover, according to this embodiment, a field judgment
signal generated by the signal generator 208 is input to the
amount-of-emitted light control means 277.
FIG. 57A shows a configuration of the light source unit 276. A lamp
281 is connected to a power supply 282 and light emission control
circuit 283. The lamp 281 is thus controlled to emit a given amount
of light. A disk-like filter member 284 is located on an optical
path of illumination light in front of the lamp 281. The filter
member 284 has an axial member attached to the center thereof. The
axial member is coupled to an axis of rotation of a motor 286 that
rotates with a motor driving signal sent from a motor drive control
circuit 285. The filter member 284 is therefore driven to rotate
together with the motor 286.
The motor drive control circuit 285 is powered by the power supply
282. A field judgment signal is sent from the image processing unit
207', and then input to the motor drive control circuit 285. The
motor drive control circuit 285 drives the motor 286 to rotate
synchronously with the signal. Moreover, the power supply 282 is
plugged into the mains or an external power source. Moreover, a
control signal sent from the light adjusting circuit 279 in the
image processing unit 207' is input to the light emission control
circuit 283.
The filter member 284 is, as shown in FIG. 57B, composed of filters
Fa and Fb offering different transmittances. For example, the
transmittance of the filter Fb is set to a one-third of the
transmittance of the filter Fa.
The other components are nearly identical to those of the ninth
embodiment.
In this embodiment, the motor 286 is rotated synchronously with a
field judgment signal shown in FIG. 58A. The filters Fa and Fb are,
as shown in FIG. 58B, alternately inserted into the optical path of
illumination light in front of the lamp 281 during respective field
periods.
When the filter Fa is placed on the optical path, an amount of
light emitted from the lamp 281 in the light source unit 276
increases as shown in FIG. 58C (the amount of emitted light is
large). When the filter Fb is placed on the optical path, the
amount of light emitted from the lamp 281 in the light source unit
276 decreases (the amount of emitted light is small).
The amount of emitted light is thus set to be different between two
field periods. The object of observation 202 is therefore
illuminated with an amount of light that is different between the
two field periods. An amount of light reflecting from the object of
observation 202 and falling on the imaging device 206 becomes
different between the two field periods.
According to this embodiment, an amount of illumination light is
controlled in order to control an amount of light incident on the
imaging device 206.
Moreover, according to this embodiment, the light adjusting circuit
279 integrates components of a luminance signal which are sent from
the image processing unit 210 during, for example, one frame
period, and thus detects an average luminance level. The average
luminance level is compared with a standard luminance level. An
error signal indicating an error from the standard luminance level
is output as a control signal, which is used to adjust light, to
the light emission control circuit 283. The light emission control
circuit 283 then controls, for example, an amount of light emitted
from the lamp 281.
For example, the average luminance level calculated by integrating
the components of the luminance signal sent during one frame period
may be lower than the standard luminance level. In this case, a
control signal proportional to an error from the standard luminance
level is input to the light emission control circuit 83. Control is
thus given in order to increase a glow current to be supplied from
the light emission control circuit 283 to the lamp 281.
Owing to the control, the average luminance level is approached to
the standard value. Consequently, a view image suitable for
observation can be constructed.
Moreover, the light adjusting circuit 279 controls an AGC circuit
in the image processing circuit 210 in terms of gain control. For
example, the AGC circuit may be allowed to control a gain in order
to attain a luminance level suitable for observation transiently
(quickly). Thereafter, control is given to emit light slowly in
order to attain an amount of light suitable for observation.
Accordingly, the AGC circuit returns a gain to a steady-state
value.
FIG. 59 shows a configuration of a light source unit 276' of a
variant. The light source unit 276' has a liquid crystal device
(LCD) 288 stationed in front of the lamp 281 shown in FIG. 57A. The
LCD 288 is controlled by a LCD drive unit 289. The other components
are identical to those shown in FIG. 57A.
The LCD 288 is driven according to the timing indicated in FIGS.
54A to 54C or FIGS. 55A to 55C.
Moreover, the operations and advantages of this variant are almost
the same as those of the twelfth embodiment.
Thirteenth Embodiment
Next, the thirteenth embodiment of the present invention will be
described.
In the twelfth embodiment, the amount-of-emitted light control
means 277 is located in front of the light emitting means in the
light source unit 276. As another method of controlling an amount
of emitted light, a method of controlling an amount of emitted
light by controlling an amount of light emanating from the light
emitting means is conceivable.
In this method, an amount of light emanating from a light emitter
is controlled according to arbitrary timing. For forming an image
prone to streaky whitening, the light emitter is allowed to glow
fully. For forming an image prone to blackening, the light emitter
is controlled to glow minimally. The timing of switching amounts of
emitted light is synchronized with the timing of switching fields
that constitute a display image. Consequently, an image prone to
streaky whitening and an image prone to blackening can be formed to
render the fields. When an algorithm set in the image processing
unit is optimized, an image proving a wide dynamic range can be
provided.
Moreover, a motion picture is not always required for image
observation. For example, when photography is carried out, a still
image may be needed. In the case of the still image, an image
proving a wide dynamic range is often not necessary. A region to be
photographed should merely be illuminated to attain a brightness
level suitable for photography. Even if the other region becomes
hard to see, no problem occurs. On such an occasion, an image not
proving a wide dynamic range will do. Another mode is therefore set
so that an image can be displayed in the mode (within ongoing
normal screen levels) instead of a wide dynamic range mode. When
the modes can thus be switched, whichever of a motion picture and
still image that is suitable for observation can be presented to a
viewer.
According to this embodiment, the light emitting means 275 in the
light source unit 276 in the twelfth embodiment is caused to emit
pulsed light. An amount of light is thus varied depending on a
field. Imaging is carried out in this state. FIG. 60 shows a
configuration of an endoscopic imaging apparatus 290 of the
thirteenth embodiment.
A camera head 293 serving as an imaging unit is mounted on an
optical endoscope 292 including an observation optical system 291.
An output signal of the imaging device 206 in the camera head 293
is input to an image processing unit 207". The image processing
unit 207" has a light adjustment and light emission signal
correcting circuit 279' that substitutes for the light adjusting
circuit 279 in the image processing unit 207' shown in FIG. 56.
The light adjustment and light emission signal correcting circuit
279' has not only the capability of the light adjusting circuit 279
but also the ability to correct a glow signal as mentioned
later.
A light guide 294 in the optical endoscope 292 is coupled to a
light source unit 295 by way of a light guide cable 278. A lamp 296
serves as a light emitting means and is included in the light
source unit 295. The lamp 296 is driven to glow by a light emission
drive unit 297. The light emission drive unit 297 is controlled by
a light emission control circuit 298.
The light emission control circuit 298 uses the light emission
drive unit 297 to control light emission of the lamp 296 according
to a field judgment signal sent from the signal generator 208 and a
light emission timing control signal. The other components are
identical to those shown in FIG. 22. The description of the
components will be omitted.
Next, the actions of this embodiment will be described with
reference to the timing charts of FIGS. 61A to 61D. The lamp
serving as a light emitting means in this embodiment glows to emit
one kind of pulsed light.
A practical example of this embodiment will be described on the
assumption that the frequency of causing the lamp 296 to glow
during a field period is varied.
The signal generator 208 in the image processing unit 207' produces
a pulsating light emission timing control signal shown in FIG. 61B
according to a field judgment signal shown in FIG. 61A. The light
emission timing control signal generated by the signal generator
208 is output to the light emission control circuit 298 in the
light source unit 295.
The light emission control circuit 298 in the light source unit 295
outputs a light emitter control signal. The light emitter control
signal causes the lamp, which is a light source, to glow
instantaneously at the leading edge of the light emission timing
control signal. With the light emitter control signal, the lamp 296
is driven to glow by means of the light emission drive unit
297.
In the practical example shown in FIG. 61C, three pulses of the
light emission timing control signal are generated during a first
field period (odd field period). One pulse thereof is generated
during a second field period.
When the glow characteristic of the lamp 296 is utilized, an amount
of emitted light varies as shown in FIG. 61C. When the amount of
emitted light varying from field to field is averaged, it varies as
shown in FIG. 61D. An amount of illumination light to be irradiated
to the object of observation 202 differs in average amount of light
from field to field. In this state, an object image is formed by
the imaging device during each field period. Consequently, an image
prone to streaky whitening is formed during a first field period
and an image prone to blacking is formed during a second field
period.
Two thus formed images are synthesized with each other by the
dynamic range expander 244 shown in FIG. 7. This results in an
image proving a wide dynamic range. Depending on the characteristic
of a lamp, there may be a time lag after a signal prompting the
lamp to glow is output from the light emission control circuit
until the lamp comes to glow fully. In this case, a proper amount
of light will not be irradiated to an object of observation during
the time interval until the lamp comes to glow fully.
In the practical example, a proper amount of light cannot be
irradiated to an object of observation for some time after
horizontal scanning for rendering a first field is started. During
the time interval, an upper portion of a display area on a typical
TV monitor beyond an upper quarter of the display area thereon is
scanned to draw 31 to 71 horizontal scanning lines. However, a
proper amount of light cannot be irradiated to an object of
observation during the time interval. An image proving a wide
dynamic range cannot therefore be displayed in the portion of the
display are on the typical TV monitor.
For coping with the foregoing drawback, a field judgment signal and
image signal are input to the light adjustment and light emission
signal correcting circuit 279' in the image processing unit 207".
For each horizontal scanning line, a luminance level is compared
with a luminance level indicated by a signal component rendering
the previous horizontal scanning line. If there is a marked
difference between the luminance levels, a light emission timing
control signal that will slightly lead the field judgment signal is
generated in order to absorb the foregoing time lag. Namely, the
time lag occurs due to the characteristic of a lamp when the lamp
is driven.
Moreover, when the amount-of-emitted light control means in the
light source unit 295 is merely driven according to a field
judgment signal, a proper amount of light may not be irradiated
entirely to an object of observation. Depending on the
characteristic of a light emitting means, it may take too much time
until the light emitting means, for example, a lamp comes to glow
fully after it is driven. On such an occasion, a sufficient amount
of light required for observation may not be preserved.
An amount of light emitted by the light source unit 295 must be
sufficient and proper for observation. For this purpose, a glow
signal correcting circuit is incorporated in the image processing
unit 107". The glow signal correcting circuit corrects a control
signal, which is output from the image processing unit 207" to the
light source unit 295, according to image information output from
the imaging device 206. Imaging can thus be performed by the
imaging device 206 so that the timing of the imaging will always be
matched with an amount of light emitted from the light source unit
295.
A method of producing a picture signal to be output to a TV monitor
or the like is identical to that employed in the ninth
embodiment.
Moreover, according to this embodiment, a freeze switch that is not
shown may be included. The freeze switch is used to send a write
disabling signal to a frame memory in the color separation and
white balance and AGC circuit 245 shown in, for example, FIG. 38.
An image whose data has been written immediately previously is
output repeatedly. The image is then displayed on an image display
means such as a TV monitor.
Moreover, this embodiment has been described that the light
emission control circuit 298 allows the lamp to glow in response to
a light emission timing control signal generated by the signal
generator 208. Alternatively, the number of pulsed light rays to be
emitted may be able to be set manually. In this case, the number of
pulsed light rays to be emitted should be able to be set for each
of two field periods. In a special example or mode, the numbers of
pulsed light rays to be emitted during the two field periods may be
set to the same value. In other words, the amounts of light to be
emitted during the two field periods may be set to the same value.
A dynamic range is not expanded in this mode.
For example, a DIP switch composed of a plurality of switching
elements may be used to input a plurality of digital signals as a
pulsed light instruction signal to the signal generator 208. The
signal generator 208 then outputs a light emission timing control
signal to the light emission control circuit 298 according to the
timing defined by the number of pulses of the pulsed light
instruction signal.
For example, when a noteworthy portion of an object to be observed
in a still image must be set to a brightness value permitting easy
observation, it can be observed in a wide dynamic range mode.
However, if a change in brightness level of the portion is
suppressed in the wide dynamic range mode, a viewer may manually
set an amount of emitted light suitable for observation. A proper
view image may thus be constructed.
Moreover, the method of manually instructing the number of pulsed
light rays to be emitted may not be adopted. Instead, an
instruction signal instructing increase or decrease of a current
number of pulsed light rays may be manually input to the signal
generator 208. A light emission timing control signal may then be
output to the light emission control circuit 298 according to the
instruction signal.
According to this embodiment, the same advantages as those of the
twelfth embodiment can be provided. Moreover, whether a motion
picture or still image is requested, an image formed with a proper
exposure value can be provided to a viewer.
According to the imaging method employed in this embodiment,
similarly to that employed in the tenth embodiment, a wheel-shaped
(disk-like) color filter may be attached to the front surface of
the imaging device.
An exposure value is controlled according to a technique of
discriminating among the transmittances of filters of three primary
colors constituting the wheel-shaped color filter. Otherwise, a
technique of differentiating the transmittance of one filter from
the transmittances of the other two filters may be adopted for
controlling an exposure value. Thus, an image proving a wide
dynamic range can be provided.
Moreover, the number of color filters constituting a filter is
three. Alternatively, two kinds of color filters offering different
transmittances may be provided for each color of three primary
colors. Red, green, and blue color filters offering high
transmittances, and red, green, and blue color filters offering low
transmittances may then be arranged equidistantly on a wheel-shaped
member. An image prone to streaky whitening and an image prone to
blacking are formed for each of the three primary colors by the
imaging device. Thereafter, the aforesaid procedure is followed and
an image proving a wide dynamic range is constructed.
Owing to the aforesaid configuration, an image proving a wide
dynamic range can be provided for a user. This means that an image
helpful in observing an object can be displayed over a whole
screen. Consequently, treatment or the like can be carried out
appropriately.
Moreover, imaging modes may be changed according to an image to be
displayed on an image display. Thus, an image helpful in observing
an object may be provided for a viewer.
As described above, according to the ninth to thirteenth
embodiments, there is provided an endoscopic imaging apparatus
consisting of: an imaging unit having an imaging device, which
receives light reflected from an object of observation and forms an
image of the object of observation during first and second imaging
periods, incorporated in an endoscope; an image processing unit for
processing signals representing first and second images formed
during the first and second imaging periods, and constructing one
synthetic image proving an expanded dynamic range by synthesizing
the first and second images; and a display means for displaying the
synthetic image.
An amount-of-incident light control means is included for
controlling an amount of light incident on the imaging device
during at least one of the first and second imaging periods. The
amount of incident light is controlled so that it will be different
from one imaging period to the other. The imaging periods need
therefore not be set to mutually greatly different lengths. Merely
by controlling the amount of light incident on the imaging device,
a view image proving a wide dynamic range can be constructed using
images formed with different amounts of light. Moreover, the view
image is unsusceptible to noises, and enjoys good image
quality.
Of course the aforesaid embodiments may be partly combined to
construct embodiments that also belong to the present
invention.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses will become apparent to those skilled
in the art. Therefore, the present invention is to be limited not
by the specific disclosure herein, but only by the appended
claims.
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